全文获取类型
收费全文 | 110675篇 |
免费 | 8457篇 |
国内免费 | 6968篇 |
专业分类
126100篇 |
出版年
2024年 | 216篇 |
2023年 | 1451篇 |
2022年 | 3244篇 |
2021年 | 5480篇 |
2020年 | 3582篇 |
2019年 | 4379篇 |
2018年 | 4358篇 |
2017年 | 3230篇 |
2016年 | 4603篇 |
2015年 | 6684篇 |
2014年 | 7868篇 |
2013年 | 8325篇 |
2012年 | 9973篇 |
2011年 | 8882篇 |
2010年 | 5453篇 |
2009年 | 4755篇 |
2008年 | 5589篇 |
2007年 | 4927篇 |
2006年 | 4373篇 |
2005年 | 3343篇 |
2004年 | 2938篇 |
2003年 | 2532篇 |
2002年 | 2210篇 |
2001年 | 2001篇 |
2000年 | 1861篇 |
1999年 | 1845篇 |
1998年 | 1021篇 |
1997年 | 1139篇 |
1996年 | 1017篇 |
1995年 | 920篇 |
1994年 | 942篇 |
1993年 | 666篇 |
1992年 | 993篇 |
1991年 | 840篇 |
1990年 | 614篇 |
1989年 | 559篇 |
1988年 | 485篇 |
1987年 | 412篇 |
1986年 | 388篇 |
1985年 | 391篇 |
1984年 | 211篇 |
1983年 | 197篇 |
1982年 | 137篇 |
1981年 | 114篇 |
1980年 | 107篇 |
1979年 | 115篇 |
1978年 | 78篇 |
1977年 | 60篇 |
1974年 | 74篇 |
1972年 | 62篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
181.
182.
183.
C. S. Wang B. S. Yandell J. J. Rutledge 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1991,82(4):421-424
Summary A bias correction was derived for the maximum likelihood estimator (MLE) of the intraclass correlation. The bias consisted of two parts: a correction from MLE to the analysis of variance estimator (ANOVA) and the bias of ANOVA. The total possible bias was always negative and depended upon both the degree of correlation and the design size and balance. The first part of the bias was an exact algebraic expression from MLE to ANOVA, and the corrected estimator by this part was ANOVA. It was also shown that the first correction term was equivalent to Fisher's reciprocal bias correction on hisZ scores. The total possible bias of MLE was large for small and moderate samples. Relative biases were larger for small parametric values and vice versa. To ensure a relative bias less than 10% assuming an intraclass correlation of 0.025, which is not unusual in most of the animal genetic studies, the total number of observations (N) should be not less than 500. From a design point of view, minimum bias occurred atn = 2, the minimum family size possible, underN fixed. 相似文献
184.
H-2M3 encodes the MHC class I molecule presenting the maternally transmitted antigen of the mouse 总被引:6,自引:0,他引:6
Mta, the maternally transmitted antigen of mice, is a hydrophobic, N-formylated mitochondrial peptide, MTF, presented on the cell surface to cytotoxic T lymphocytes by a novel major histocompatibility complex class I molecule, encoded by H-2M3. We have cloned and sequenced two alleles of M3, which differ in their ability to present MTF despite greater than 99% identity in the coding regions. M3 is as divergent from classical, antigen-presenting H-2 molecules as from other class I genes of the Hmt and the Qa/Tla regions. Amino acids critical for folding of class I molecules are conserved in M3. Noncharged amino acids lining the peptide-binding groove and phenylalanine 171 may explain the unique interaction with MTF, and leucine 95 appears critical for immunological activity. 相似文献
185.
Shui-Tein Chen Shiah-Yun Chen Shu-Chyong Hsiao Kung-Tsung Wang 《Biotechnology letters》1991,13(11):773-778
Summary An industrial alkaline protease Alcalase has been found to be very stable in organic solvents and usable as a catalyst for resolution of N-protected amino acids, in both aqueous solution and organic solvent with high yield and optical purity. Only the L-amino acid ester has been hydrolysed.Abbreviation Cbz-
carbobenzyloxy-
- OMe
methyl ester
- Hop
homophenylalanine
- Nol
norleucine
- Aba
-amino butyric acid
- Nov
norvaline
- Fug
furylglycine 相似文献
186.
Expression and stability of amplified genes encoding 5-enolpyruvylshikimate-3-phosphate synthase in glyphosate-tolerant tobacco cells 总被引:10,自引:0,他引:10
Yunxia Wang James D. Jones Stephen C. Weller Peter B. Goldsbrough 《Plant molecular biology》1991,17(6):1127-1138
Two distinct cDNAs for 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) were obtained from a glyphosate-tolerant tobacco cell line. The cDNAs were 89% identical and the predicted sequences of the mature proteins were greater than 83% identical with EPSPS proteins from other plants. Tobacco EPSPS proteins were more similar to those from tomato and petunia than Arabidopsis. One cDNA clone, EPSPS-1, represented a gene that was amplified in glyphosate-tolerant cells, while the gene for EPSPS-2 was unaltered in these cells. Consequently, EPSPS-1 mRNA was more abundant in tolerant than unselected cells, whereas EPSPS-2 mRNA was at relatively constant levels in these cell lines. Exposure of unselected cells and tobacco leaves to glyphosate produced a transient increase in EPSPS mRNA. However, glyphosate-tolerant cells containing amplified copies of EPSPS genes did not show a similar response following exposure to glyphosate. A significant proportion of the EPSPS gene amplification was maintained when tolerant cells were grown in the absence of glyphosate for eight months. Plants regenerated from these cells also contained amplified EPSPS genes. 相似文献
187.
188.
J. J. Wang S. R. Roffler M. H. Yu C. S. Yin M. Y. Yeh 《Histochemistry and cell biology》1992,97(6):453-461
Summary The specific binding and nature of the epitope recognized by monoclonal antibody (Mab) 1H10, which binds an antigen expressed on human cervical tumors, was characterized by enzyme digestion, lectin competition assay and immuno-electron microscopy. Membrane homogenates of CaSki cervical carcinoma cells were digested with various enzymes, then analysed by SDS-PAGE and immunoblotting. Cells grown on coverslips were treated with various enzymes and in situ binding of Mab 1H10 to cells was analysed by electron microscopy. The ability of lectin-conjugates to block Mab 1H10 binding to CaSki cells was also examined. Treatment of samples with sodium periodate abrogated antigen recognition by Mab 1H10. Neuraminidase and hyaluronidase digestion decreased but did not eliminate Mab 1H10 binding to cells in situ. Chondroitinase ABC digestion, in contrast, removed Mab 1H10 binding sites both in vitro and in situ. Trypsin and chymotrypsin digestion of cell membrane homogenates decreased the molecular weight of the Mab 1H10 antigen but did not decrease the binding intensity. Wheat germ agglutinin (WGA) strongly bound to CaSki cells and partially blocked Mab 1H10 binding, indicating that the antigen contains N-acetyl-galactosamine residues at or near the epitope recognized by Mab 1H10. Ricinus communis agglutinin (RCA) exhibited a similar binding pattern to WGA. However, concanavalin A bound only weakly to CaSki cells and was ineffective at blocking Mab 1H10 binding. The tumor-associated antigen recognized by Mab 1H10 is concluded to be a chondroitin sulphate glycoprotein or proteoglycan rather than a mucopolysaccharide or lipoprotein. 相似文献
189.
The plasma membrane calcium pump: a multiregulated transporter 总被引:6,自引:0,他引:6
Activation of many cells, especially nonexcitable cells, results in a Ca(2+) transient that is influenced in part by the kinetics of active extrusion of Ca(2+) across the plasma membrane. The molecular cloning of the plasma membrane Ca(2+)-pump has helped to clarify the relationship between its structure and function. The Ca(2+)-pump is controlled by multiple regulators, including calmodulin, phospholipids and various kinases. Longer term control is achieved through regulation of its gene expression, and the presence of a number of Ca(2+)-pump isoforms that differ in their regulatory domains provides potential functional diversity. In this review, we focus on the mechanisms that regulate the function of the Ca(2+)-pump, and their physiological significance. 相似文献
190.