全文获取类型
收费全文 | 6818篇 |
免费 | 813篇 |
国内免费 | 3篇 |
专业分类
7634篇 |
出版年
2022年 | 43篇 |
2021年 | 109篇 |
2020年 | 55篇 |
2019年 | 78篇 |
2018年 | 63篇 |
2017年 | 72篇 |
2016年 | 144篇 |
2015年 | 249篇 |
2014年 | 279篇 |
2013年 | 313篇 |
2012年 | 472篇 |
2011年 | 494篇 |
2010年 | 271篇 |
2009年 | 269篇 |
2008年 | 415篇 |
2007年 | 444篇 |
2006年 | 404篇 |
2005年 | 425篇 |
2004年 | 408篇 |
2003年 | 429篇 |
2002年 | 381篇 |
2001年 | 76篇 |
2000年 | 50篇 |
1999年 | 103篇 |
1998年 | 121篇 |
1997年 | 86篇 |
1996年 | 86篇 |
1995年 | 75篇 |
1994年 | 81篇 |
1993年 | 71篇 |
1992年 | 55篇 |
1991年 | 55篇 |
1990年 | 47篇 |
1989年 | 45篇 |
1988年 | 45篇 |
1987年 | 61篇 |
1986年 | 40篇 |
1985年 | 47篇 |
1984年 | 63篇 |
1983年 | 56篇 |
1982年 | 83篇 |
1981年 | 52篇 |
1980年 | 54篇 |
1979年 | 40篇 |
1978年 | 27篇 |
1977年 | 39篇 |
1976年 | 22篇 |
1975年 | 22篇 |
1974年 | 19篇 |
1968年 | 19篇 |
排序方式: 共有7634条查询结果,搜索用时 0 毫秒
1.
A group of captive chimpanzees, consisting of one adult male and three mother/infant pairs, was systematically observed over a 15-month period. Over 200 hr of data were collected, using both sequential and time sampling techniques, and compared to the available data on wild chimps. Unlike many captive groups, most behavior patterns were remarkably similar, both qualitatively and quantitatively, to that of wild chimpanzees including: play, grooming, infant sexual development, tool use, food sharing, prosocial partner preferences, and aggressive displays. 相似文献
2.
Nancy Burton Wurster George Lust 《Biochimica et Biophysica Acta (BBA)/General Subjects》1984,800(1):52-58
The content and the biosynthesis of fibronectin was examined in disease-free articular cartilage and in articular cartilage from osteoarthritic canine joints. Fibronectin content was increased in extracts of cartilage from osteoarthritic joints. Incubation of cartilage in vitro with [3H]phenylalanine and subsequent isolation of [3H]fibronectin from a gelatin affinity column and characterization by SDS-polyacrylamide gel electrophoresis and by immunoprecipitation indicated that disease-free and osteoarthritic cartilage explants synthesized fibronectin. About 50% of the [3H]fibronectin was recovered in the incubation medium. The osteoarthritic cartilage synthesized and accumulated up to 5-fold more [3H]fibronectin than disease-free cartilage. 相似文献
3.
Douglas G. Gilmour Walter M. Collins Tom L. Fredericksen Willard E. Urban Jr. Paul F. Ward Nancy L. DiFronzo 《Immunogenetics》1986,23(1):1-6
Chickens of Regional Poultry Research Laboratory (RPRL) inbred line 63 regress sarcomas induced by Bryan high-titer Rous sarcoma virus to a greater extent than chickens of line RPRL 100, although these lines are identical for the major histocompatibility B complex. They differ, however, at three independent autosomal loci: Ly-4 and Th-1 determine the surface alloantigens of partly overlapping subsets of T lymphocytes, and Bu-1 determines a surface alloantigen of B lymphocytes. The association of genotypes at these loci with quantitative variation in their ability to regress Rous sarcomas was tested in segregating F4 generation progeny derived from crosses of lines 100 and 63. The Ly-4 and Bu-1 genotypes showed association with Rous sarcoma regression, but the Th-1 genotype did not. Chickens of the Ly-4
a/Ly-4
a, Bu-1
b/Bu-1
b and Ly-4
b/Ly-4
b, Bu-1
a/Bu-1
a genotypes had a significantly higher regressor ability than the other two double homozygous genotypes. These results indicate that higher regression is associated with (1) interaction between the Ly-4 and Bu-1 loci, and (2) complementation between either the line 6 Ly-4
a allele and the line 100 Bu-1
b allele, or the line 100 Ly-4
b allele and the line 6 Bu-1
a allele. 相似文献
4.
Lois B. Epstein Mary E. Rose Nancy H. McManus 《Biochemical and biophysical research communications》1982,104(1):341-346
A comparison of the amino acid sequence of one human recombinant IFN-α (IFLrA) with either human β-endorphin or ACTH reveals only a minimal and insignificant degree of homology. Also, synthetic ACTH, β-endorphin and β-endorphin-(1–15) have no antiviral protective effects on human fibroblasts and cannot inhibit the neutralization of the antiviral effects of natural IFN-α by an antiserum directed against the interferon. Anti ACTH and Anti β-endorphin do not neutralize the antiviral effects of IFLrA, and radioimmunoassays of partially purified natural IFN-α and pure IFLrA do not reveal any evidence of α-MSH or β-endorphin-like material in the interferons. These results demonstrate an absence of functional and structural homology of natural and recombinant IFN-α with ACTH and β-endorphin. 相似文献
5.
Nancy Steinberg Warren 《American journal of human genetics》1992,51(1):224-225
6.
Expression of renal cell protein markers is dependent on initial mechanical culture conditions. 总被引:4,自引:0,他引:4
Nancy L Cowger Edmund Benes Patricia L Allen Timothy G Hammond 《Journal of applied physiology》2002,92(2):691-700
The rotating wall vessel is optimized for suspension culture, with laminar flow and adequate nutrient delivery, but minimal shear. However, higher shears may occur in vivo. During rotating wall vessel cultivation of human renal cells, size and density of glass-coated microcarrier beads were changed to modulate initial shear. Renal-specific proteins were assayed after 2 days. Flow cytometry antibody binding analysis of vitamin D receptor demonstrated peak expression at intermediate shears, with 30% reduction outside this range. Activity of cathepsin C showed the inverse pattern, lowest at midshear, with twofold increases at either extreme. Dipeptidyl-peptidase IV had no shear dependence, suggesting that the other results are specific, not universal, changes in membrane trafficking or protein synthesis. On addition of dextran, which changes medium density and viscosity but not shear, vitamin D receptor assay showed no differences from controls. Neither cell cycle, apoptosis/necrosis indexes, nor lactate dehydrogenase release varied between experiments, confirming that the changes are primary, not secondary to cell cycling or membrane damage. This study provides direct evidence that mechanical culture conditions modulate protein expression in suspension culture. 相似文献
7.
8.
9.
The 13C NMR spectra of geosmin, selina-4(14),7(11)-diene-99-ol and two dihydroeudesmol isomers have been obtained and the individual resonances assigned. Several different empirical correlations developed by others have been combined in simple calculations to predict chemical shift values for sesquiterpenols of the eudesmane group. 相似文献
10.