全文获取类型
收费全文 | 153476篇 |
免费 | 24104篇 |
国内免费 | 9702篇 |
专业分类
187282篇 |
出版年
2024年 | 275篇 |
2023年 | 1726篇 |
2022年 | 3842篇 |
2021年 | 6673篇 |
2020年 | 6028篇 |
2019年 | 8393篇 |
2018年 | 8424篇 |
2017年 | 7439篇 |
2016年 | 9020篇 |
2015年 | 11374篇 |
2014年 | 12576篇 |
2013年 | 13498篇 |
2012年 | 13441篇 |
2011年 | 11959篇 |
2010年 | 9330篇 |
2009年 | 7441篇 |
2008年 | 7435篇 |
2007年 | 6312篇 |
2006年 | 5597篇 |
2005年 | 4452篇 |
2004年 | 4016篇 |
2003年 | 3545篇 |
2002年 | 3148篇 |
2001年 | 2741篇 |
2000年 | 2448篇 |
1999年 | 2356篇 |
1998年 | 1274篇 |
1997年 | 1356篇 |
1996年 | 1224篇 |
1995年 | 1082篇 |
1994年 | 1106篇 |
1993年 | 769篇 |
1992年 | 1125篇 |
1991年 | 941篇 |
1990年 | 703篇 |
1989年 | 625篇 |
1988年 | 536篇 |
1987年 | 445篇 |
1986年 | 418篇 |
1985年 | 419篇 |
1984年 | 228篇 |
1983年 | 222篇 |
1982年 | 163篇 |
1981年 | 126篇 |
1980年 | 116篇 |
1979年 | 124篇 |
1978年 | 86篇 |
1977年 | 66篇 |
1974年 | 79篇 |
1972年 | 67篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Application of macroscopic balances to the identification of gross measurement errors 总被引:1,自引:0,他引:1
A systematic method is presented which is capable of both detecting the presence of grossly biased measurement errors and locating the source of these errors in a bioreactor through statistical hypothesis testing. Equality constraints derived from material and energy balances are employed for the detection of data inconsistencies and for the subsequent identification of the suspect measurements by a process of data analysis and rectification. Maximum likelihood techniques are applied to the estimation of the states and parameters of the bioreactor after the suspect measurements have been eliminated. The level of significance is specified by the experimenter while the measurments are assumed to be randomly, normally distributed with zero mean and known variances. Two different approaches of data analysis, batchwise and sequential, that lead to a consistent set of adjustments on the experimental values, are discussed. Several examples based on the fermentation data taken from literature sources are presented to demonstrate the utility of the proposed method, and one set of data is solved numerically to illustrate the computational aspect of the algorithm. 相似文献
62.
63.
Some properties of phospholipases of alveolar macrophages 总被引:6,自引:0,他引:6
64.
65.
66.
67.
给家兔喂以1%胆固醇及10%菜油(A组)或猪油(B组)50多天后A组血胆固醇水平(824.2±265.1mg/dl)明显低于B组(1666±693.8mg/dl);A组甘油三酯水平(51.9±19.1mg/dl)亦低于B组(104±40.2mg/dl)。二组家兔的β—VLDL的脂类组成无差别,但A组β—VLDL的apoE高于B组,分别为45.2%及37.5%。高分子量apoB(apoB_h)为33.6%,低于B组β-VLDL(47.3%)。A组β-VLDL促进小鼠腹腔巨噬细胞胆固醇堆积的程度大于B组,可能与apoE含量高有关。我们认为多不饱和脂酸减轻动脉粥样硬化(As)的作用不在于改变脂蛋白构成后阻碍泡沫细胞的形成而是促进β—VLDL从体内清除。 相似文献
68.
Second virial coefficient of alpha-crystallin 总被引:1,自引:0,他引:1
Light scattering studies were performed on bovine alpha-crystallin measuring the scattering intensities as a function of scattering angle, concentration, and temperature. The data yielded the molecular weight, radius of gyration, and second virial coefficient of alpha-crystallin at different temperatures. The second virial coefficient increased with increasing temperature. Both the enthalpy and entropy of solution of alpha-crystallin are positive. The Flory theta temperature was found to be 271 K. 相似文献
69.
Phenotype frequencies for the complement proteins C4A, C4B, Bf (factor B) and C3 were performed for 49 Caucasian patients with psoriasis. The C4*A6 allele was present in 26.6% of the patients as compared to 5.4% of healthy regional Caucasian controls, p less than 0.001, relative risk = 6.28. The C4*A6 allele is known to be in linkage disequilibrium with the HLA B17 allele and to produce a non-functional gene product when it occurs with the B17 allele. HLA B17 is known to be associated with psoriasis in many Caucasian populations. Additional findings in the present study were a significant reduction in the C4B*2 allele frequency, a non-significant increase in the Bf*F allele frequency and no difference for Bf or C3 phenotype frequencies in the patients with psoriasis as compared to the controls. 相似文献
70.
Transposon mutagenesis of baculoviruses: analysis of TFP3 lepidopteran transposon insertions at the FP locus of nuclear polyhedrosis viruses 总被引:3,自引:0,他引:3
We report the complete sequences of two representatives of the TFP3 transposable element family of the lepidopteran, Trichoplusia ni. These elements were isolated as insertions mobilized from the Lepidopteran host genome into two closely related nuclear polyhedrosis viruses (NPV) during infection. Both elements inserted within the 500-bp FP locus of the respective viral genomes (map units 36.0 to 37.0), causing a distinctive plaque morphology phenotype and the loss of a 25-kDa viral-specific protein. Both insertions occurred at the identical TTAA target site in the respective genomes, in the same relative orientation, and are flanked by 15-bp imperfect inverted repeats. The inserted elements interrupt the 25K open reading frame (ORF). One of these FP mutants undergoes spontaneous reversion. Sequence analysis at the excision site of a spontaneous revertant demonstrates that the TFP3 elements are capable of precise excision, restoring the expression of the 25-kDa protein. We also compare the sequences of the 25K genes of the Autographa californica and Galleria mellonella viruses (AcMNPV and GmMNPV, respectively). The 25K gene sequences diverge in five areas, resulting in an additional EcoRV and TaqI site within the GmMNPV 25K gene, and extension of the ORF for an additional 2 amino acids at the C-terminus of the predicted GmMNPV 25 kDa protein. The phenomenon of transposon mutagenesis of Baculovirus genomes provides a unique opportunity for analysis of transposon mobility. 相似文献