首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5564篇
  免费   627篇
  国内免费   655篇
  2024年   20篇
  2023年   57篇
  2022年   148篇
  2021年   278篇
  2020年   239篇
  2019年   287篇
  2018年   257篇
  2017年   209篇
  2016年   262篇
  2015年   365篇
  2014年   398篇
  2013年   429篇
  2012年   528篇
  2011年   472篇
  2010年   312篇
  2009年   280篇
  2008年   282篇
  2007年   292篇
  2006年   246篇
  2005年   209篇
  2004年   202篇
  2003年   221篇
  2002年   162篇
  2001年   131篇
  2000年   95篇
  1999年   83篇
  1998年   87篇
  1997年   41篇
  1996年   38篇
  1995年   22篇
  1994年   16篇
  1993年   14篇
  1992年   30篇
  1991年   18篇
  1990年   30篇
  1989年   22篇
  1988年   8篇
  1987年   9篇
  1986年   4篇
  1985年   3篇
  1984年   6篇
  1983年   4篇
  1982年   3篇
  1981年   4篇
  1980年   2篇
  1979年   2篇
  1976年   2篇
  1973年   2篇
  1972年   5篇
  1958年   2篇
排序方式: 共有6846条查询结果,搜索用时 62 毫秒
111.
Wilted black poplar, Populus nigra ‘Italica’ L., leaves are very attractive to a vast number of noctuid moth species. This provides an opportunity for the development of effective trapping methods for the integrated management of pest species, such as Helicoverpa armigera, a major global and economically important insect pest.In the present study, we investigated the (1) nocturnal attraction patterns of H. armigera males and females to wilted P. nigra leaves; (2) effects of P. nigra volatiles on the mate-searching behavior of males through laboratory serial-chamber bioassays and field trapping; and (3) effects of P. nigra volatiles on the ovipositional choice and reproductive performance of females. Females and males, when tested alone, could be attracted by wilted P. nigra leaves, and the time periods of the first two attraction peaks were largely overlapped between sexes. Streams consisting of wilted P. nigra leaves and virgin females were not more attractive than virgin females alone, regardless of the stream sequence in a serial chamber. However, a stream of virgin females passed through wilted P. nigra leaves was more attractive than wilted P. nigra leaves alone. The addition of P. nigra extracts and its major aromatic components to the sex lure of H. armigera did not attract more moths than the sex lure alone. The volatiles from wilted P. nigra leaves were significantly more attractive to ovipositing females than those from cotton, tomato, and corn leaves, but equally attractive to tobacco leaves. Females exposed to volatiles from different leaves (P. nigra, cotton, and tobacco) showed similar fecundities. In summary, the attraction of moths to wilted P. nigra leaves may be attributable to multiple mechanisms, including the adsorption of sex pheromones, ovipostional attraction, and possible feeding attraction.  相似文献   
112.
Molecular Breeding - The stem color of young mung bean is a very useful tool in germplasm identification. Flowering time and plant height (PH) are known to be strongly correlated with crop adaption...  相似文献   
113.
Entomopathogenic fungi such as Metarhizium rileyi and Beauveria bassiana are widely used insect biological control agents. Little, however, is known concerning genetic or enzymatic factors that differentiate the mechanisms employed by these two fungal pathogens to infect target hosts. Infection by either of these organisms is known to increase levels of the growth and molting hormone, ecdysone, which also regulates the expression of a number of innate immune pathways. M. rileyi, but not B. bassiana, has apparently evolved an ecdysteroid-22-oxidase (MrE22O) that inactivate ecdysone. We show that deletion of MrE22O impaired virulence compared with the wild-type strain, with an increase in ecdysone titer seen in hosts that was coupled to an increase in the expression of antimicrobial genes. An M. rileyi strain engineered to overexpress MrE22O (MrE22OOE), as well as trans-expression in B. bassiana (Bb::MrE220OE) resulted, in strains displaying enhanced virulence and dampening of host immune responses compared with their respective wild-type parental strains. These results indicate that ecdysone plays an important role in mediating responses to fungal infection and that some insect pathogenic fungi have evolved mechanisms for targeting this hormone as a means for facilitating infection.  相似文献   
114.
Shan  Mingqiu  Jiang  Yulan  Fu  Yuanyuan  Zhou  Yongyi  Lu  Zhihui  Yu  Sheng  Yan  Hui  Liu  Chanchan  Chen  Peidong  Bao  Beihua  Zhang  Li  Wu  Qinan 《Phytochemistry Reviews》2021,20(5):991-1012
Phytochemistry Reviews - Nepeta tenuifolia (N. tenuifolia) is a common aromatic herb that is widespread in East Asia. The aerial parts and spikes can be used as the traditional phytomedicines for...  相似文献   
115.
Huang  Wei  Cao  Yu  Chen  Chenyang  Wu  Xi  Sheng  Zhe  Li  Anying 《Journal of molecular histology》2021,52(4):767-780
Journal of Molecular Histology - Myocardial infarction (MI) is a great threat to patients all over the word. MicroRNAs (miRNAs) are a group of non-coding RNAs and can regulate initiation and...  相似文献   
116.
采用溶液培养方法,研究不同浓度硝酸铈对花生(Arachis hypogaea)幼苗生长、开花数目及抗氧化酶过氧化物酶(POD)、超氧化物歧化酶(SOD)活性与丙二醛(MDA)含量的影响。结果表明,与对照相比,铈浓度低于20.0 mg·L–1能促进花生幼苗生长及开花,其中以10.0 mg·L–1铈的效果最为明显,其生物量和开花数分别约为对照的1.3倍和2.8倍;但高于20.0 mg·L–1则抑制花生幼苗生长,降低花朵数目;同时,低于20.0 mg/L铈可抑制花生幼苗过氧化物酶(POD)活性和降低其丙二醛(MDA)含量,其中以10.0 mg·L–1铈的抑制效果最明显,其POD活性和MDA含量约为对照的47.51%和20.76%;而低于20.0 mg·L–1铈能提高花生幼苗的超氧化物歧化酶(SOD)活性,其中以5.0 mg·L–1铈的促进效果最明显,其SOD活性约为对照的2.0倍。  相似文献   
117.
Ferritin is a conserved iron-binding protein involved in cellular iron metabolism and host defense. In the present study, two distinct cDNAs for ferritins in the freshwater pearl mussel Hyriopsis schlegelii were identified (designated as HsFer-1 and HsFer-2) by SMART RACE approach and expressed sequence tag (EST) analysis. The full-length cDNAs of HsFer-1 and HsFer-2 were of 760 and 877 bp, respectively. Both of the two cDNAs contained an open reading frame (ORF) of 522 bp encoding for 174 amino acid residues. Sequence characterization and homology alignment indicated that HsFer-1 and HsFer-2 had higher similarity to H-type subunit of vertebrate ferritins than L-type subunit. Analysis of the HsFer-1 and HsFer-2 untranslated regions (UTR) showed that both of them had an iron response element (IRE) in the 5′-UTR, which was considered to be the binding site for iron regulatory protein (IRP). Quantitative real-time PCR (qPCR) assays were employed to examine the mRNA expression profiles. Under normal physiological conditions, the expression level of both HsFer-1 and HsFer-2 mRNA were the highest in hepatopancreas, moderate in gonad, axe foot, intestine, kidney, heart, gill, adductor muscle and mantle, the lowest in hemocytes. After stimulation with bacteria Aeromonas hydrophila, HsFer-1 mRNA experienced a different degree of increase in the tissues of hepatopancreas, gonad and hemocytes, the peak level was 2.47-fold, 9.59-fold and 1.37-fold, respectively. Comparatively, HsFer-2 showed up-regulation in gonad but down-regulation in hepatopancreas and hemocytes. Varying expression patterns indicate that two types of ferritins in H. schlegelii might play different roles in response to bacterial challenge. Further bacteriostatic analysis showed that both the purified recombinant ferritins inhibited the growth of A. hydrophila to a certain degree. Collectively, our results suggest that HsFer-1 and HsFer-2 are likely to be functional proteins involved in immune defense against bacterial infection.  相似文献   
118.
Fatty acid–binding protein 3 (FABP3) facilitates the movement of fatty acids in cardiac muscle. Previously, we reported that FABP3 is highly upregulated in the myocardium of ventricular septal defect patients and overexpression of FABP3 inhibited proliferation and promoted apoptosis in embryonic carcinoma cells (P19 cells). In this study, we aimed to investigate the effect of FABP3 gene silencing on P19 cell differentiation, proliferation and apoptosis. We used RNA interference and a lentiviral-based vector system to create a stable FABP3-silenced P19 cell line; knockdown of FABP3 was confirmed by quantitative real-time PCR. Expression analysis of specific differentiation marker genes using quantitative real-time PCR and observation of morphological changes using an inverted microscope revealed that knockdown of FABP3 did not significantly affect the differentiation of P19 cells into cardiomyocytes. CCK-8 proliferation assays and cell cycle analysis demonstrated that FABP3 gene silencing significantly inhibited P19 cell proliferation. Furthermore, Annexin V-FITC/propidium iodide staining and the caspase-3 activity assay revealed that FABP3 gene silencing significantly promoted serum starvation–induced apoptosis in P19 cells. In agreement with our previous research, these results demonstrate that FABP3 may play an important role during embryonic heart development, and that either overexpression or silencing of FABP3 will lead to an imbalance between proliferation and apoptosis, which may result in embryonic cardiac malformations.  相似文献   
119.
This study was conducted to evaluate the relationship between the flora and the changes in the microbial communities during tomato paste wastewater treatment. The bio-analytical techniques like Polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE), adenosine-triphosphate (ATP) analysis, and testing of mixed liquid and suspended solids (MLSS) were simultaneously conducted to analyze the dynamics of the microbial communities during tomato paste wastewater treatment process. The study suggests that the combined approaches of PCR-DGGE, ATP, and MLSS provided a simple and accurate method to evaluate the changes in microbial activity, microbial structure, and population size with the shift in contaminants in different treatment processes. The study also demonstrates that the structure and quantity of a microbial community are influenced by MLSS during the wastewater treatment process, which consequently determines the overall functionality of the system.  相似文献   
120.
The current in-depth proteomics makes use of long chromatography gradient to get access to more peptides for protein identification, resulting in covering of as many as 8000 mammalian gene products in 3 days of mass spectrometer running time. Here we report a fast sequencing (Fast-seq) workflow of the use of dual reverse phase high performance liquid chromatography - mass spectrometry (HPLC-MS) with a short gradient to achieve the same proteome coverage in 0.5 day. We adapted this workflow to a quantitative version (Fast quantification, Fast-quan) that was compatible to large-scale protein quantification. We subjected two identical samples to the Fast-quan workflow, which allowed us to systematically evaluate different parameters that impact the sensitivity and accuracy of the workflow. Using the statistics of significant test, we unraveled the existence of substantial falsely quantified differential proteins and estimated correlation of false quantification rate and parameters that are applied in label-free quantification. We optimized the setting of parameters that may substantially minimize the rate of falsely quantified differential proteins, and further applied them on a real biological process. With improved efficiency and throughput, we expect that the Fast-seq/Fast-quan workflow, allowing pair wise comparison of two proteomes in 1 day may make MS available to the masses and impact biomedical research in a positive way.The performance of mass spectrometry has been improved tremendously over the last few years (13), making mass spectrometry-based proteomics a viable approach for large-scale protein analysis in biological research. Scientists around the world are striving to fulfill the promise of identifying and quantifying almost all gene products expressed in a cell line or tissue. This would make mass spectrometry-based protein analysis an approach that is compatible to the second-generation mRNA deep-seq technique (4, 5).Two liquid chromatography (LC)-MS strategies have been employed to achieve deep proteome coverage. One is a single run with a long chromatography column and gradient to take advantage of the resolving power of HPLC to reduce the complexity of peptide mixtures; the other is a sequential run with two-dimensional separation (typically ion-exchange and reverse phase) to reduce peptide complexity. It was reported by two laboratories that 2761 and 4500 proteins were identified with a 10 h chromatography gradient on a dual pressure linear ion-trap orbitrap mass spectrometer (LTQ Orbitrap Velos)(68). Similarly, 3734 proteins were identified using a 8 h gradient on a 2 m long column with a hybrid triple quadrupole - time of flight (Q-TOF, AB sciex 5600 Q-TOF)(9) mass spectrometer. The two-dimensional approach has yielded more identification with longer time. For example, 10,006 proteins (representing over 9000 gene products, GPs)1 were identified in U2OS cell (10), and 10,255 proteins (representing 9207 GPs) from HeLa cells (11). It took weeks (for example, 2–3 weeks) of machine running time to achieve such proteome coverage, pushing proteome analysis to the level that is comparable to mRNA-seq. With the introduction of faster machines, human proteome coverage now has reached the level of 7000–8500 proteins (representing 7000–8000 GPs) in 3 days (12). Notwithstanding the impressive improvement, the current approach using long column and long gradient suffers from inherent limitations: it takes long machine running time and it is challenging to keep reproducibility among repeated runs. Thus, current throughput and reproducibility have hindered the application of in-depth proteomics to traditional biological researches. A timesaving approach is in urgent need.In this study, we used the first-dimension (1D) short pH 10 RP prefractionation to reduce the complexity of the proteome (13), followed by sequential 30 min second-dimension (2D) short pH 3 reverse phase-(RP)-LC-MS/MS runs for protein identification (14). The results demonstrated that it is possible to identify 8000 gene products from mammalian cells within 12 h of total MS measurement time by applying this dual-short 2D-RPLC-MS/MS strategy (Fast sequencing, Fast-seq). The robustness of the strategy was revealed by parallel testing on different MS systems including quadrupole orbitrap mass spectrometer (Q-Exactive), hybrid Q-TOF (Triple-TOF 5600), and dual pressure linear ion-trap orbitrap mass spectrometer (LTQ-Orbitrap Velos), indicating the inherent strength of the approach as to merely taking advantage of the better MS instruments. This strategy increases the efficiency of MS sequencing in unit time for the identification of proteins. We achieved identification of 2200 proteins/30 mins on LTQ-Orbitrap Velos, 2800 proteins/30 mins on Q-Exactive and Triple-TOF 5600 respectively. We further optimized Fast-seq and worked out a quantitative-version of the Fast-seq workflow: Fast-quantification (Fast-quan) and applied it for protein abundance quantification in HUVEC cell that was treated with a drug candidate MLN4924 (a drug in phase III clinical trial). We were able to quantify > 6700 GPs in 1 day of MS running time and found 99 proteins were up-regulated with high confidence. We expect this efficient alternative approach for in-depth proteome analysis will make the application of MS-based proteomics more accessible to biological applications.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号