全文获取类型
收费全文 | 86786篇 |
免费 | 7687篇 |
国内免费 | 43篇 |
专业分类
94516篇 |
出版年
2023年 | 282篇 |
2022年 | 712篇 |
2021年 | 1558篇 |
2020年 | 886篇 |
2019年 | 1118篇 |
2018年 | 1453篇 |
2017年 | 1253篇 |
2016年 | 2152篇 |
2015年 | 3645篇 |
2014年 | 4074篇 |
2013年 | 4855篇 |
2012年 | 6591篇 |
2011年 | 6519篇 |
2010年 | 4200篇 |
2009年 | 3817篇 |
2008年 | 5460篇 |
2007年 | 5475篇 |
2006年 | 5268篇 |
2005年 | 5061篇 |
2004年 | 4937篇 |
2003年 | 4699篇 |
2002年 | 4432篇 |
2001年 | 902篇 |
2000年 | 673篇 |
1999年 | 1000篇 |
1998年 | 1244篇 |
1997年 | 828篇 |
1996年 | 752篇 |
1995年 | 666篇 |
1994年 | 632篇 |
1993年 | 672篇 |
1992年 | 571篇 |
1991年 | 540篇 |
1990年 | 471篇 |
1989年 | 423篇 |
1988年 | 439篇 |
1987年 | 356篇 |
1986年 | 325篇 |
1985年 | 407篇 |
1984年 | 529篇 |
1983年 | 411篇 |
1982年 | 508篇 |
1981年 | 491篇 |
1980年 | 420篇 |
1979年 | 305篇 |
1978年 | 339篇 |
1977年 | 288篇 |
1976年 | 268篇 |
1975年 | 216篇 |
1974年 | 249篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
71.
72.
73.
Michael J. Hynes 《Journal of genetics》1996,75(3):297-311
Many filamentous fungi of all taxa can now be subject to DNA-mediated transformation. Many dominant selectable markers are available and the range available is increasing as new genes are cloned. Transformation is especially valuable in cloning genes defined by mutations with selectable phenotypes and is allowing investigation of many problems in fungi with good genetic systems. Increasingly sophisticated techniques for inactivating genes, targetingin vitro generated mutations to specific loci, and altering gene expression and its regulation are being developed. These approaches are being used to investigate the wealth of basic and applied biological problems available in filamentous fungi. 相似文献
74.
Aspartate, glutamate, or dicarboxylic acids did not inhibit the activity of a highly purified but not homogeneous preparation of pyruvate carboxylase fromThiobacillus novellus. The only effective inhibitors were end-products of the reaction and to a lesser degree hydroxypyruvate. The latter has not been shown previously to regulate the enzyme's activity. Lineweaver-Burk plots revealed that it was uncompetitive with respect to acetyl CoA with a Kii of 3.6 mM, and noncompetitive with respect to bicarbonate, magnesium ATP, and pyruvate with respective Kii values of 7.1, 5.5, and 6.47 mM. The corresponding Kis values were 7.02, 5.4, and 4.25 mM. A mathematical model is presented that supports the findings. 相似文献
75.
Cory Bystrom Shijun Sheng Ke Zhang Michael Caulfield Nigel J. Clarke Richard Reitz 《PloS one》2012,7(9)
Measurement of insulin-like growth factor-1 (IGF-I) has utility for the diagnosis and management of growth disorders, but inter-assay comparison of results has been complicated by a multitude of reference standards, antibodies, detection methods, and pre-analytical preparation strategies. We developed a quantitative LC-MS method for intact IGF-I, which has advantages in throughput and complexity when compared to mass spectrometric approaches that rely on stable isotope dilution analysis of tryptic peptides. Since the method makes use of full-scan data, the assay was easily extended to provide quantitative measurement of IGF-II using the same assay protocol. The validated LC-MS assay for IGF-I and IGF-II provides accurate results across the pediatric and adult reference range and is suitable for clinical use. 相似文献
76.
77.
78.
79.
Chemokines and their ligands play a critical role in enabling chronic lymphocytic leukaemia (CLL) cells access to protective microenvironmental niches within tissues, ultimately resulting in chemoresistance and relapse: disruption of these signaling pathways has become a novel therapeutic approach in CLL. The tyrosine kinase inhibitor dasatinib inhibits migration of several cell lines from solid-organ tumours, but effects on CLL cells have not been reported. We studied the effect of clinically achievable concentrations of dasatinib on signaling induced by the chemokine CXCL12 through its'' receptor CXCR4, which is highly expressed on CLL cells. Dasatinib pre-treatment inhibited Akt and ERK phosphorylation in CLL cells upon stimulation with CXCL12. Dasatinib also significantly diminished the rapid increase in actin polymerisation observed in CLL cells following CXCL12 stimulation. Moreover, the drug significantly inhibited chemotaxis in a transwell assay, and reduced the percentage of cells able to migrate beneath a CXCL12-expressing murine stromal cell line. Dasatinib also abrogated the anti-apoptotic effect of prolonged CXCL12 stimulation on cultured CLL cells. These data suggest that dasatinib, akin to other small molecule kinase inhibitors targeting the B-cell receptor signaling pathway, may redistribute CLL cells from protective tissue niches to the peripheral blood, and support the investigation of dasatinib in combination strategies. 相似文献
80.
Alfalfa (Medicago sativa L. cv. Vernal) nodules were separatedinto host plant fractions and fractions of rhizobial originby differential centrifugation and sedimentation equilibriumcentrifugation. Both NAD- and NADP-linked isocitrate dehydrogenase(70%, 90%) and glutamate dehydrogenase activities (90%, 83%)were located primarily (percent total nodule activity) in thefractions of plant origin and their specific activities werehighest in the fractions of plant origin. More than 50% of thenodules' total activity of both glutamine synthetase and NAD-glutamatesynthase and greater than 90% of the total glutamate oxaloacetatetransaminase activity was located in plant fractions. However,the fractions of rhizobial origin had the highest specific activitiesof glutamine synthetase and glutamate synthase. (Received September 5, 1981; Accepted December 7, 1981) 相似文献