全文获取类型
收费全文 | 13993篇 |
免费 | 1354篇 |
国内免费 | 295篇 |
出版年
2023年 | 82篇 |
2022年 | 175篇 |
2021年 | 379篇 |
2020年 | 262篇 |
2019年 | 313篇 |
2018年 | 313篇 |
2017年 | 285篇 |
2016年 | 468篇 |
2015年 | 690篇 |
2014年 | 731篇 |
2013年 | 867篇 |
2012年 | 1083篇 |
2011年 | 1029篇 |
2010年 | 602篇 |
2009年 | 487篇 |
2008年 | 730篇 |
2007年 | 612篇 |
2006年 | 589篇 |
2005年 | 550篇 |
2004年 | 553篇 |
2003年 | 439篇 |
2002年 | 434篇 |
2001年 | 321篇 |
2000年 | 310篇 |
1999年 | 312篇 |
1998年 | 156篇 |
1997年 | 137篇 |
1996年 | 110篇 |
1995年 | 103篇 |
1994年 | 99篇 |
1993年 | 99篇 |
1992年 | 198篇 |
1991年 | 145篇 |
1990年 | 159篇 |
1989年 | 157篇 |
1988年 | 173篇 |
1987年 | 126篇 |
1986年 | 122篇 |
1985年 | 142篇 |
1984年 | 109篇 |
1983年 | 77篇 |
1982年 | 62篇 |
1981年 | 57篇 |
1980年 | 53篇 |
1979年 | 98篇 |
1978年 | 86篇 |
1977年 | 69篇 |
1976年 | 55篇 |
1974年 | 61篇 |
1973年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 266 毫秒
841.
Background
Nasal strips are used by athletes, people who snore, and asthmatics to ease the burden of breathing. Although there are some published studies that demonstrate higher flow with nasal strips, none had directly measured the effect of the strips on nasal resistance using the airflow perturbation device (APD). The APD is an inexpensive instrument that can measure respiratory resistance based on changes in mouth pressure and rate of airflow. 相似文献842.
Dasuri K Antonovici M Chen K Wong K Standing K Ens W El-Gabalawy H Wilkins JA 《Arthritis research & therapy》2004,6(2):R161-R168
The present studies were initiated to determine the protein expression patterns of fibroblast-like synovial (FLS) cells derived
from the synovia of rheumatoid arthritis patients. The cellular proteins were separated by two-dimensional polyacrylamide
gel electrophoresis and the in-gel digested proteins were analyzed by matrix-assisted laser desorption ionization mass spectrometry.
A total of 368 spots were examined and 254 identifications were made. The studies identified a number of proteins that have
been implicated in the normal or pathological FLS function (e.g. uridine diphosphoglucose dehydrogenase, galectin 1 and galectin
3) or that have been characterized as potential autoantigens in rheumatoid arthritis (e.g. BiP, colligin, HC gp-39). A novel
uncharacterized protein product of chromosome 19 open reading frame 10 was also detected as an apparently major component
of FLS cells. These results demonstrate the utility of high-content proteomic approaches in the analysis of FLS composition. 相似文献
843.
A way to control the average pore size in cross-linked polyacrylamide-based membranes is by altering the ratio of cross-linker to acylamide monomer. Larger pore sizes are prepared with a minimum amount of cross-linker, resulting in membranes that are mechanically weak and have short lifetimes. The aim of this study was to prepare cross-linked polyacrylamide membranes with large pore sizes and with good mechanical integrity. The methodology was to carry out the polymerization in a template, formed from the self-aggregation of surfactant. Two surfactant templates were used, and their pore size was examined with proteins of different sizes. The surfactants chosen for this study were sodium dodecyl sulfate (SDS, ionic surfactant) and TERIC BL8 (nonionic surfactant), both of which have very different aggregation properties. The data showed that at 10% and greater of TERIC BL8, a very different and open gel structure is formed, in which the pore size was significantly increased. SDS seemed to have little effect on the pore size. The data suggests that the gel structures for both surfactants up to 4% (w/v) are similar and micellular, because SDS is known to favor a micelle structure. Above 4% (w/v), TERIC BL8 then goes through a change in its lyotropic phase, thus, producing membranes of a large pore size. In conclusion, the pore size and gel structure of polyacrylamide hydrogel membranes can be significantly increased using TERIC BL8 (nonionic) surfactant. This allows large-pore-size membranes with a high cross-link density and consequently high mechanical strength to be prepared for the separation of large biomolecules. 相似文献
844.
The central nervous system (CNS) is a major dose-limiting organ in clinical radiotherapy (XRT). The underlying mechanisms of radiation-induced injury in this organ remain unclear. For many years, research has focused on identifying the major target cells of damage, and depletion of target cells due to reproductive or clonogenic cell death was believed to be the primary cause of tissue damage and organ failure. There is now an increasing body of data indicating that the response of the CNS after XRT is a continuous and interacting process. This review addresses some of the recent advances in our understanding of the mechanisms of CNS radiation damage. Specifically, the focus is on apoptotic cell death, and cell death and injury mediated by secondary damage. These potentially reversible components of the injury response provide important targets for neuroprotective interventions. 相似文献
845.
Wong BB Salzmann C Schiestl FP 《Proceedings. Biological sciences / The Royal Society》2004,271(Z4):S212-S214
Orchids are extraordinary among plants because many species are pollinated through sexual duplicity by producing flowers that mimic female insects to lure unsuspecting males. Previous work showed that sexual deception by the orchid Chiloglottis trapeziformis can have a negative impact on its wasp pollinator Neozeleboria cryptoides. We report that female wasps may be capable of mitigating the cost of the orchids' deception. Although male wasps quickly habituated to areas planted with unrewarding flower decoys, we found that the effectiveness of the chemical cue used by the wingless females to attract males increases with increasing distance from an orchid patch. The apparent specificity of the males' site-based avoidance strategy means that females emerging in areas occupied by flowering orchids could, potentially, leave the orchid colony by walking to increase their attractiveness. 相似文献
846.
Lingling?Wang Li?Ma Wenchuan?Leng Jian?Yang Junping?Zhu Jie?Dong Ying?Xue Zhe?Wan Ruoyu?Li Qi?JinEmail author 《中国科学C辑(英文版)》2004,47(5):389-395
Trichophyton rubrum (T. rubrum) is the most common of the superficial fungi. In an effort to better understand the genetic and biochemical makeup ofT. rubrum, we generated cDNA libraries from 3 growth stages and used these to isolate 4002 unique expressed sequence tags (ESTs). Sequence
comparisons with the Genbank database allowed 1226 of the ESTs to be assigned putative functions or matched with homologs
from other organisms. Of the remaining ESTs, 989 were only weakly similar to known sequences and 1787 had no identifiable
functions, suggesting that they represent novel genes. We further analyzed the presence of several important genes involved
in the growth, metabolism, signal transduction, pathogenesis and drug resistance inT. rubrum. This information was used to newly elucidate important metabolic pathways inT. rubrum. Taken together, our results should form the molecular basis for continued research on the physiological processes and pathogenic
mechanisms ofT. rubrum, and may lead to a better understanding of fungal drug resistance and identification of new drug targets. 相似文献
847.
It often is assumed that more distant allopatry should reflect reduced rates of contemporary gene flow and/or greater divergence in mate recognition systems. This assumption, however, is rarely tested and may not always be appropriate. Here we investigated female preference for local and foreign males in a morphologically variable Australian freshwater fish, the Pacific blue-eye Pseudomugil signifer. Using a multidisciplinary approach that combined molecular phylogeography with conventional mate choice experiments, we found female blue-eyes spent more time in association with local males only when the alternative was a foreigner from a geographically and genetically more distant population. When offered the choice between two foreign males, females associated more with males from the population that was more closely adjacent to their own. Our results suggest that female preference for local over foreign males in blue-eyes may depend on how genetically and geographically separated populations are from one another. 相似文献
848.
Han ZM Chen DY Li JS Sun QY Wan QH Kou ZH Rao G Lei L Liu ZH Fang SG 《Molecular reproduction and development》2004,67(2):207-214
Adult somatic cell cloned calves were produced by somatic cell nuclear transfer prepared by fusion of cultured ear fibroblast from a Holstein cow into enucleated oocytes of Luxi Yellow cow. In order to determinate the source of mitochondrial DNA of cloned calves, we designed the breed-specific PCR primers by aligning the known D-loop sequences of Bos taurus and analyzed the displacement loop sequences of five live cloned calves by breed-specific primers PCR. The results demonstrated that mtDNA originated from Holstein breed and that from Luxi breed co-exist in all five live calves. 相似文献
849.
P-type ATPase heavy metal transporters with roles in essential zinc homeostasis in Arabidopsis 总被引:20,自引:0,他引:20
下载免费PDF全文
![点击此处可从《The Plant cell》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Hussain D Haydon MJ Wang Y Wong E Sherson SM Young J Camakaris J Harper JF Cobbett CS 《The Plant cell》2004,16(5):1327-1339
Arabidopsis thaliana has eight genes encoding members of the type 1B heavy metal–transporting subfamily of the P-type ATPases. Three of these transporters, HMA2, HMA3, and HMA4, are closely related to each other and are most similar in sequence to the divalent heavy metal cation transporters of prokaryotes. To determine the function of these transporters in metal homeostasis, we have identified and characterized mutants affected in each. Whereas the individual mutants exhibited no apparent phenotype, hma2 hma4 double mutants had a nutritional deficiency phenotype that could be compensated for by increasing the level of Zn, but not Cu or Co, in the growth medium. Levels of Zn, but not other essential elements, in the shoot tissues of a hma2 hma4 double mutant and, to a lesser extent, of a hma4 single mutant were decreased compared with the wild type. Together, these observations indicate a primary role for HMA2 and HMA4 in essential Zn homeostasis. HMA2promoter- and HMA4promoter-reporter gene constructs provide evidence that HMA2 and HMA4 expression is predominantly in the vascular tissues of roots, stems, and leaves. In addition, expression of the genes in developing anthers was confirmed by RT-PCR and was consistent with a male-sterile phenotype in the double mutant. HMA2 appears to be localized to the plasma membrane, as indicated by protein gel blot analysis of membrane fractions using isoform-specific antibodies and by the visualization of an HMA2-green fluorescent protein fusion by confocal microscopy. These observations are consistent with a role for HMA2 and HMA4 in Zn translocation. hma2 and hma4 mutations both conferred increased sensitivity to Cd in a phytochelatin-deficient mutant background, suggesting that they may also influence Cd detoxification. 相似文献
850.
Voynow JA Fischer BM Malarkey DE Burch LH Wong T Longphre M Ho SB Foster WM 《American journal of physiology. Lung cellular and molecular physiology》2004,287(6):L1293-L1302
Goblet cell hyperplasia in the superficial airway epithelia is a signature pathological feature of chronic bronchitis and cystic fibrosis. In these chronic inflammatory airway diseases, neutrophil elastase (NE) is found in high concentrations in the epithelial lining fluid. NE has been reported to trigger mucin secretion and increase mucin gene expression in vitro. We hypothesized that chronic NE exposure to murine airways in vivo would induce goblet cell metaplasia. Human NE (50 microg) or PBS saline was aspirated intratracheally by male Balb/c (6 wk of age) mice on days 1, 4, and 7. On days 8, 11, and 14, lung tissues for histology and bronchoalveolar lavage (BAL) samples for cell counts and cytokine levels were obtained. NE induced Muc5ac mRNA and protein expression and goblet cell metaplasia on days 8, 11, and 14. These cellular changes were the result of proteolytic activity, since the addition of an elastase inhibitor, methoxysuccinyl Ala-Ala-Pro-Val chloromethylketone (AAPV-CMK), blocked NE-induced Muc5ac expression and goblet cell metaplasia. NE significantly increased keratinocyte-derived chemokine and IL-5 in BAL and increased lung tissue inflammation and BAL leukocyte counts. The addition of AAPV-CMK reduced these measures of inflammation to control levels. These experiments suggest that NE proteolytic activity initiates an inflammatory process leading to goblet cell metaplasia. 相似文献