全文获取类型
收费全文 | 9898篇 |
免费 | 749篇 |
国内免费 | 260篇 |
出版年
2024年 | 15篇 |
2023年 | 85篇 |
2022年 | 207篇 |
2021年 | 323篇 |
2020年 | 234篇 |
2019年 | 288篇 |
2018年 | 328篇 |
2017年 | 221篇 |
2016年 | 388篇 |
2015年 | 559篇 |
2014年 | 652篇 |
2013年 | 701篇 |
2012年 | 885篇 |
2011年 | 850篇 |
2010年 | 499篇 |
2009年 | 469篇 |
2008年 | 584篇 |
2007年 | 554篇 |
2006年 | 441篇 |
2005年 | 379篇 |
2004年 | 396篇 |
2003年 | 337篇 |
2002年 | 272篇 |
2001年 | 190篇 |
2000年 | 184篇 |
1999年 | 132篇 |
1998年 | 54篇 |
1997年 | 67篇 |
1996年 | 71篇 |
1995年 | 46篇 |
1994年 | 41篇 |
1993年 | 34篇 |
1992年 | 64篇 |
1991年 | 53篇 |
1990年 | 39篇 |
1989年 | 28篇 |
1988年 | 36篇 |
1987年 | 25篇 |
1986年 | 18篇 |
1985年 | 20篇 |
1984年 | 15篇 |
1983年 | 18篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 10篇 |
1977年 | 6篇 |
1976年 | 8篇 |
1975年 | 7篇 |
1973年 | 7篇 |
1971年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
71.
72.
广东鼎湖山季风常绿阔叶林的主要优势乔木树种荷木和黧蒴幼苗生长于自然光照和人工调节CO2浓度为500±50μl·L-1或空气CO2(350μl·L-1)的气罩中3个月。高CO2浓度下生长的黧蒴和荷木植株总干物质量分别增加26.6%和16.6%,根部增加量最大,地上部分所占的比例降低,根冠比上升,基径增大而株高降低。高CO2浓度下生长的叶片密度及比叶重增加,叶肉细胞间隙体积减少。单位干重的黧蒴叶片可溶性糖含量、全碳、磷、钾含量在高CO2浓度下稍为下降,果糖、葡萄糖、蔗糖、全氮、镁含量及N/C比明显降低。而全钙含量无明显变化。 相似文献
73.
Weidong Jiang Moon-Young Lim Hye-Joo Yoon Jeremy Thorner G. Steven Martin John Carbon 《Molecular & general genetics : MGG》1995,246(3):360-366
We find that overexpression in yeast of the yeast MCK1 gene, which encodes a meiosis and centromere regulatory kinase, suppresses the temperature-sensitive phenotype of certain mutations in essential centromere binding protein genes CBF2 and CBF5. Since Mck1p is a known serine/threonine protein kinase, this suppression is postulated to be due to Mck1p-catalyzed in vivo phosphorylation of centromere binding proteins. Evidence in support of this model was provided by the finding that purified Mck1p phosphorylates in vitro the 110 kDa subunit (Cbf2p) of the multimeric centromere binding factor CBF3. This phosphorylation occurs on both serine and threonine residues in Cbf2p. 相似文献
74.
We used quantitative complementation assays to characterize individual DNA polymerase (Pol) mutants for their ability to function in DNA replication and DNA repair. We also describe a screen for detecting imitator activity of DNA polymerase mutants. By using these bioassays, together with DNA polymerase activity gels, we characterized 15 new DNA polymerase mutants that display a wide spectrum of phenotypes. Most of these mutants are generally defective in their ability to synthesize DNA. However, two of our Pol mutants show more complex phenotypes: they are able to function in DNA repair but unable to participate in DNA replication. One of our mutants displays imitator activity in vivo. Our work provides a model to study mutant mammalian enzymes inEscherichia coli with phenotypes that are otherwise difficult to assess. 相似文献
75.
Genetic variation of herpesvirus saimiri subgroup A transforming protein and its association with cellular src. 总被引:2,自引:2,他引:0
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
H Lee J J Trimble D W Yoon D Regier R C Desrosiers J U Jung 《Journal of virology》1997,71(5):3817-3825
Herpesvirus saimiri strain 11 of subgroup A contains a gene called the saimiri transformation-associated protein, STP, which is not required for viral replication but is required for in vitro immortalization and for the lymphoma-inducing capacity of the virus. To assess the effects of sequence variation on STP function, STP genes from six subgroup A isolates were cloned and sequenced. Sequence comparisons revealed extensive amino acid substitutions within the central region, but the acidic amino terminus and the hydrophobic carboxyl terminus were well conserved. Amino acid identities varied from 73 to 99% among all two-way comparisons. The highly conserved YAEV/I motif at amino acid residues 115 to 118 was preceded by negatively charged glutamic acid residues and thus matched very well the consensus sequence for binding to SH2 domains of src family kinases. The STPs of these subgroup A strains were shown to associate with cellular src and to be an in vitro substrate for src kinase. Mutational analysis of STP-A11 showed that binding to src kinase required the tyrosine residue at 115, showing that YAEV/I is a likely binding motif for src. Also, tyrosine phosphorylation of STP-A11 by src led to subsequent binding to lck and fyn in vitro. Thus, the association of STP with src is likely to be important for T-cell transformation by subgroup A strains of herpesvirus saimiri. 相似文献
76.
Possible role of macrophage-derived soluble mediators in the pathogenesis of encephalomyocarditis virus-induced diabetes in mice. 总被引:4,自引:1,他引:3
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
K Hirasawa H S Jun K Maeda Y Kawaguchi S Itagaki T Mikami H S Baek K Doi J W Yoon 《Journal of virology》1997,71(5):4024-4031
Pancreatic islets from DBA/2 mice infected with the D variant of encephalomyocarditis (EMC-D) virus revealed lymphocytic infiltration with moderate to severe destruction of pancreatic beta cells. Our previous studies showed that the major population of infiltrating cells at the early stages of infection is macrophages. The inactivation of macrophages prior to viral infection resulted in the prevention of diabetes, whereas activation of macrophages prior to viral infection resulted in the enhancement of beta-cell destruction. This investigation was initiated to determine whether macrophage-produced soluble mediators play a role in the destruction of pancreatic beta cells in mice infected with a low dose of EMC-D virus. When we examined the expression of the soluble mediators interleukin-1 beta (IL-1beta), tumor necrosis factor alpha (TNF-alpha), and inducible nitric oxide synthase (iNOS) in the pancreatic islets, we found that these mediators were clearly expressed at an early stage of insulitis and that this expression was evident until the development of diabetes. We confirmed the expression of these mediators by in situ hybridization with digoxigenin-labelled RNA probes or immunohistochemistry in the pancreatic islets. Mice treated with antibody against IL-1beta or TNF-alpha or with the iNOS inhibitor aminoguanidine exhibited a significant decrease in the incidence of diabetes. Mice treated with a combination of anti-IL-1beta antibody, anti-TNF-alpha antibody, and aminoguanidine exhibited a greater decrease in the incidence of disease than did mice treated with one of the antibodies or aminoguanidine. On the basis of these observations, we conclude that macrophage-produced soluble mediators play an important role in the destruction of pancreatic beta cells, resulting in the development of diabetes in mice infected with a low dose of EMC-D virus. 相似文献
77.
K Abrahamsen H L Kong A Mastrangeli D Brough A Lizonova R G Crystal E Falck-Pedersen 《Journal of virology》1997,71(11):8946-8951
A strategy for constructing replication-defective adenovirus vectors from non-subgroup C viruses has been successfully demonstrated with adenovirus type 7 strain a (Ad7a) as the prototype. An E1A-deleted Ad7a reporter virus expressing the chloramphenicol acetyltransferase (CAT) gene from the cytomegalovirus promoter enhancer was constructed with DNA fragments isolated from Ad7a, an Ad7a recombination reporter plasmid, and the 293 cell line. The Ad7a-CAT virus particle transduces A549 cells as efficiently as Ad5-based vectors. Intravenous infections in a murine model indicate that the Ad7a-CAT virus infects a variety of tissues, with maximal levels of CAT gene expression found in the liver. The duration of Ad7a-CAT transgene expression in the liver was maximally maintained 2 weeks postinfection, with a decline to baseline activity by the week 4 postinfection. Ad7a-CAT represents the first example of a non-subgroup C E1A- adenovirus gene transfer vector. 相似文献
78.
Phosphorylation of rat muscle acetyl-CoA carboxylase by AMP-activated protein kinase and protein kinase A 总被引:7,自引:0,他引:7
Winder W. W.; Wilson H. A.; Hardie D. G.; Rasmussen B. B.; Hutber C. A.; Call G. B.; Clayton R. D.; Conley L. M.; Yoon S.; Zhou B. 《Journal of applied physiology》1997,82(1):219-225
Winder, W. W., H. A. Wilson, D. G. Hardie, B. B. Rasmussen,C. A. Hutber, G. B. Call, R. D. Clayton, L. M. Conley, S. Yoon, and B. Zhou. Phosphorylation of rat muscle acetyl-CoA carboxylase byAMP-activated protein kinase and protein kinase A. J. Appl. Physiol. 82(1): 219-225, 1997This studywas designed to compare functional effects of phosphorylation of muscleacetyl-CoA carboxylase (ACC) by adenosine 3,5-cyclicmonophosphate-dependent protein kinase (PKA) and by AMP-activatedprotein kinase (AMPK). Muscle ACC (272 kDa) was phosphorylated and thensubjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresisfollowed by autoradiography. Functional effects of phosphorylation weredetermined by measuring ACC activity at different concentrations ofeach of the substrates and of citrate, an activator of the enzyme. Themaximal velocity(Vmax) and theMichaelis constants(Km) for ATP,acetyl-CoA, and bicarbonate were unaffected by phosphorylation by PKA.Phosphorylation by AMPK increased theKm for ATP andacetyl-CoA. Sequential phosphorylation by PKA and AMPK, first withoutlabel and second with label, appeared to reduce the extent of label incorporation, regardless of the order. The activation constant (Ka) forcitrate activation was increased to the same extent by AMPKphosphorylation, regardless of previous or subsequent phosphorylation by PKA. Thus muscle ACC can be phosphorylated by PKA but with noapparent functional effects on the enzyme. AMPK appears to be the moreimportant regulator of muscle ACC. 相似文献
79.
A greenhouse assay to screen sunflower for resistance to Alternaria helianthi is described. A comparison of conditions led to the following standard conditions being recommended. The first or second pair of leaves of seedling plants at the V8 growth stage are inoculated using inoculum grown on sunflower leaf extract agar for 5–10 days at an inoculum density of 1–2 spores cm2 of leaf tissue. A 48 h dew period should be applied to plants covered by a plastic tent. A dew period temperature of 26/26°C night/day and a post-dew period temperature relative to that experienced under local growing conditions should be applied. Lesions are measured 7 days after inoculation, and mean lesion size per plant is calculated. Mean lesion size of lines being tested is expressed as a proportion of the mean lesion size of a susceptible standard included in each screening experiment. 相似文献
80.