全文获取类型
收费全文 | 4109篇 |
免费 | 277篇 |
国内免费 | 8篇 |
专业分类
4394篇 |
出版年
2024年 | 18篇 |
2023年 | 44篇 |
2022年 | 157篇 |
2021年 | 193篇 |
2020年 | 167篇 |
2019年 | 273篇 |
2018年 | 258篇 |
2017年 | 171篇 |
2016年 | 208篇 |
2015年 | 199篇 |
2014年 | 251篇 |
2013年 | 366篇 |
2012年 | 321篇 |
2011年 | 318篇 |
2010年 | 192篇 |
2009年 | 150篇 |
2008年 | 150篇 |
2007年 | 172篇 |
2006年 | 131篇 |
2005年 | 111篇 |
2004年 | 108篇 |
2003年 | 94篇 |
2002年 | 76篇 |
2001年 | 20篇 |
2000年 | 14篇 |
1999年 | 15篇 |
1998年 | 9篇 |
1997年 | 10篇 |
1996年 | 15篇 |
1995年 | 7篇 |
1994年 | 7篇 |
1992年 | 10篇 |
1991年 | 5篇 |
1990年 | 10篇 |
1988年 | 9篇 |
1987年 | 9篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1981年 | 6篇 |
1980年 | 8篇 |
1979年 | 8篇 |
1978年 | 6篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1975年 | 6篇 |
1974年 | 5篇 |
1973年 | 6篇 |
1970年 | 4篇 |
1969年 | 4篇 |
排序方式: 共有4394条查询结果,搜索用时 15 毫秒
51.
52.
Firouzeh Bordbar Mohammad Reza Rahiminejad Hojjatollah Saeidi Frank R. Blattner 《Plant Systematics and Evolution》2011,291(1-2):117-131
Cereal species of the grass tribe Triticeae are economically important and provide staple food for large parts of the human population. The Fertile Crescent of Southwest Asia harbors high genetic and morphological diversity of these species. In this study, we analyzed genetic diversity and phylogenetic relationships among D genome-bearing species of the wheat relatives of the genus Aegilops from Iran and adjacent areas using allelic diversity at 25 nuclear microsatellite loci, nuclear rDNA ITS, and chloroplast trnL-F sequences. Our analyses revealed high microsatellite diversity in Aegilops tauschii and the D genomes of Triticum aestivum and Ae. ventricosa, low genetic diversity in Ae. cylindrica, two different Ae. tauschii gene pools, and a close relationship among Ae. crassa, Ae. juvenalis, and Ae. vavilovii. In the latter species group, cloned sequences revealed high diversity at the ITS region, while in most other polyploids, homogenization of the ITS region towards one parental type seems to have taken place. The chloroplast genealogy of the trnL-F haplotypes showed close relationships within the D genome Aegilops species and T. aestivum, the presence of shared haplotypes in up to three species, and up to three different haplotypes within single species, and indicates chloroplast capture from an unidentified species in Ae. markgrafii. The ITS phylogeny revealed Triticum as monophyletic and Aegilops as monophyletic when Amblyopyrum muticum is included. 相似文献
53.
A total of 250 broilers in a completely randomized design selected to evaluate the effect of different levels of chromium (Cr) supplementation on performance, carcass traits and some blood parameters of heat-stressed broiler chicks. All birds were kept under heat stress temperature (33?±?3°C) and divided into five treatments groups. Each treatment consisted of five pens with 10 birds in each pen. The basal diets were supplemented with 0?ppb (control), 800?ppb Cr-L-Met (T(1)), 1,200?ppb Cr-L-Met (T(2)) or 800?ppb CrCl(3) (T(3)), and 1,200?ppb CrCl(3) (T(4)). The feed intake and body mass were measured at 10, 21, and 42?days of age. Blood samples were collected from two birds in each replicates to determine biological and hematological values at 28 and 42?days of age. There were no significant difference in mass gain and feed conversion of broilers that received Cr supplementations compared with controls. The serum glucose concentration decreased in broilers received organic chromium methionine supplements compared with other treatments groups. Slight but not significant increases were observed in serum high-density lipoprotein (HDL) concentration of treated groups than controls while the mean serum HDL concentration was significantly higher in T(2) group compared with control group. Serum low-density lipoprotein level decreased in broiler received organic Cr supplements (p?0.05). 相似文献
54.
Zohreh Moradi Ali Reza Rezvani Meissam Noroozifar 《Journal of biomolecular structure & dynamics》2018,36(3):779-794
In order to evaluate biological potential of a novel synthesized complex [Nd(dmp)2Cl3.OH2] where dmp is 29-dimethyl 110-phenanthroline, the DNA-binding, cleavage, BSA binding, and antimicrobial activity properties of the complex are investigated by multispectroscopic techniques study in physiological buffer (pH 7.2).The intrinsic binding constant (Kb) for interaction of Nd(III) complex and FS–DNA is calculated by UV–Vis (Kb = 2.7 ± 0.07 × 105) and fluorescence spectroscopy (Kb = 1.13 ± 0.03 × 105). The Stern–Volmer constant (KSV), thermodynamic parameters including free energy change (ΔG°), enthalpy change (?H°), and entropy change (?S°), are calculated by fluorescent data and Vant’ Hoff equation. The experimental results show that the complex can bind to FS–DNA and the major binding mode is groove binding. Meanwhile, the interaction of Nd(III) complex with protein, bovine serum albumin (BSA), has also been studied by using absorption and emission spectroscopic tools. The experimental results show that the complex exhibits good binding propensity to BSA. The positive ΔH° and ?S° values indicate that the hydrophobic interaction is main force in the binding of the Nd(III) complex to BSA, and the complex can quench the intrinsic fluorescence of BSA remarkably through a static quenching process. Also, DNA cleavage was investigated by agarose gel electrophoresis that according to the results cleavage of DNA increased with increasing of concentration of the complex. Antimicrobial screening test gives good results in the presence of Nd(III) complex system. 相似文献
55.
C. Seth Pearson Reza Nemati Binbin Liu Jing Zhang Matteo Scalabrin Zhong Li Hongmin Li Dan Fabris Marlene Belfort Georges Belfort 《Biotechnology and bioengineering》2019,116(4):709-721
We have engineered an intein which spontaneously and reversibly forms a thiazoline ring at the native N-terminal Lys-Cys splice junction. We identified conditions to stablize the thiazoline ring and provided the first crystallographic evidence, at 1.54 Å resolution, for its existence at an intein active site. The finding bolsters evidence for a tetrahedral oxythiazolidine splicing intermediate. In addition, the pivotal mutation maps to a highly conserved B-block threonine, which is now seen to play a causative role not only in ground-state destabilization of the scissile N-terminal peptide bond, but also in steering the tetrahedral intermediate toward thioester formation, giving new insight into the splicing mechanism. We demonstrated the stability of the thiazoline ring at neutral pH as well as sensitivity to hydrolytic ring opening under acidic conditions. A pH cycling strategy to control N-terminal cleavage is proposed, which may be of interest for biotechnological applications requiring a splicing activity switch, such as for protein recovery in bioprocessing. 相似文献
56.
Maliheh Moradzadeh Mohamad Reza Kalani Amir Avan 《Journal of cellular biochemistry》2019,120(4):4732-4738
Saffron (Crocus sativus L.), and its main constituents, crocin, and crocetin have shown promising effects as an antileukemic agent in animal models and cell culture systems. Saffron retards the growth of cancer cells via inhibiting nucleic acid synthesis and enhancing antioxidative system. It can induce apoptosis and chemosensitivity via inhibiting multidrug resistance proteins. Saffron also induces differentiation pathways via inhibiting promyelocytic leukemia/retinoic acid receptor-α, histone deacetylase1, and tyrosyl DNA phosphodiesterase-1 as well. The present review highlights the most recent findings on the antileukemic effects of saffron and its underlying molecular targets. The emerging evidence suggests that saffron has a selective toxicity effect against leukemic cells while is safe for the normal cells. 相似文献
57.
J R Paulson P W Mesner J J Delrow N N Mahmoud W A Ciesielski 《Analytical biochemistry》1992,203(2):227-234
A new method is described for analysis of histone H1 and other basic proteins by cationic disc electrophoresis in polyacrylamide gels at neutral pH. The multiphasic buffer (disc) system uses Na+ as leading ion, L-histidine as trailing ion, and Hepes as buffering counterion. These "Hepes/histidine gels" have three advantages over conventional acid-urea gels for studies of H1 phosphorylation and dephosphorylation: speed, convenience, and the need for only small amounts of cells or chromatin. Core histones and their acetylated forms can also be separated in gels containing 0.4% Triton X-100. The difference in electrophoretic mobility between mitotic (superphosphorylated) and interphase H1 from HeLa cells is approximately twice as great at neutral pH as at pH 4.5, making it possible to separate these two H1 forms rapidly and easily in Hepes/histidine "minigels" only 5-cm long. Total histones can be rapidly prepared by simply neutralizing 0.2 N HCl extracts, and the entire analysis, from harvesting cells to destaining gels, can be carried out in 1 day. The stacking effect of the disc system produces sharp bands and high resolution even with relatively dilute samples. 相似文献
58.
Akram Mirzaei Sina Rashedi Mohammad Reza Akbari Fatemeh Khatami Seyed Mohammad Kazem Aghamir 《Journal of cellular and molecular medicine》2022,26(9):2728
Arsenic trioxide (ATO) and statins have been demonstrated to have anti‐neoplastic properties; however, the data regarding their combination therapy is limited. Thus, we aimed to study the effects of ATO, Simvastatin and their combination in proliferation, apoptosis and pathological angiogenesis in prostate cancer cell lines. The human prostate cell lines were treated with different concentrations of Simvastatin and ATO alone and combined to find effective doses and IC50 values. In addition, the percentage of apoptotic cells was evaluated by annexin/PI staining, and mRNA expression levels of the apoptotic gene, including OPN isoforms and VEGF, were investigated using real‐time PCR. Our data displayed that Simvastatin (12 and 8 μM in PC3 and LNCaP cell lines respectively), ATO (8 and 5 μM in PC3 and LNCaP cell lines respectively), and also their combination (12 μM Simvastatin and 8 μM ATO in PC3, 8 μM Simvastatin and 5 μM ATO in LNCaP cell lines respectively) significantly increased the percentage of apoptotic cells. Also, we showed that the combination therapy by Simvastatin and ATO increased cell apoptosis and inhibited cell proliferation, providing anti‐proliferative and anti‐angiogenic properties, possibly via downregulation of the expression of VEGF and OPN genes. These results provide new perceptions regarding the anticancer roles of ATO and statins’ combination therapy in prostate cancer. 相似文献
59.
Mahmoud A. Elfaky Alaa Sirwi Sameh H. Ismail Heba H. Awad Sameh S. Gad 《Current issues in molecular biology》2022,44(7):2923
Silver nanoparticles have been used for numerous therapeutic purposes because of their increased biodegradability and bioavailability, yet their toxicity remains questionable as they are known to interact easily with biological systems because of their small size. This study aimed to investigate and compare the effect of silver nanoparticles’ particle size in terms of their potential hazard, as well as their potential protective effect in an LPS-induced hepatotoxicity model. Liver slices were obtained from Sprague Dawley adult male rats, and the thickness of the slices was optimized to 150 μm. Under regulated physiological circumstances, freshly cut liver slices were divided into six different groups; GP1: normal, GP2: LPS (control), GP3: LPS + AgNpL (positive control), GP4: LPS + silymarin (standard treatment), GP5: LPS + AgNpS + silymarin (treatment I), GP6: LPS + AgNpL + silymarin (treatment II). After 24 h of incubation, the plates were gently removed, and the supernatant and tissue homogenate were all collected and then subjected to the following biochemical parameters: Cox2, NO, IL-6, and TNF-α. The LPS elicited marked hepatic tissue injury manifested by elevated cytokines and proinflammatory markers. Both small silver nanoparticles and large silver nanoparticles efficiently attenuated LPS hepatotoxicity, mainly via preserving the cytokines’ level and diminishing the inflammatory pathways. In conclusion, large silver nanoparticles exhibited effective hepatoprotective capabilities over small silver nanoparticles. 相似文献
60.
Mirjalili Seyedsina Tohidi Moghadam Tahereh H. Sajedi Reza 《Plasmonics (Norwell, Mass.)》2022,17(3):1269-1277
Plasmonics - Any excess or lack of human serum albumin (HSA) in urine should be considered a warning for renal or cardiovascular diseases. This report proposes a rapid and straightforward method... 相似文献