全文获取类型
收费全文 | 45435篇 |
免费 | 3675篇 |
国内免费 | 5篇 |
专业分类
49115篇 |
出版年
2023年 | 224篇 |
2021年 | 320篇 |
2020年 | 296篇 |
2019年 | 278篇 |
2018年 | 897篇 |
2017年 | 933篇 |
2016年 | 1010篇 |
2015年 | 932篇 |
2014年 | 1064篇 |
2013年 | 1908篇 |
2012年 | 3137篇 |
2011年 | 3451篇 |
2010年 | 1781篇 |
2009年 | 1152篇 |
2008年 | 2843篇 |
2007年 | 2928篇 |
2006年 | 2729篇 |
2005年 | 2426篇 |
2004年 | 2313篇 |
2003年 | 2178篇 |
2002年 | 2177篇 |
2001年 | 1505篇 |
2000年 | 1752篇 |
1999年 | 926篇 |
1998年 | 423篇 |
1997年 | 338篇 |
1996年 | 406篇 |
1995年 | 358篇 |
1994年 | 380篇 |
1993年 | 341篇 |
1992年 | 382篇 |
1991年 | 319篇 |
1990年 | 296篇 |
1989年 | 269篇 |
1988年 | 260篇 |
1987年 | 269篇 |
1986年 | 225篇 |
1985年 | 317篇 |
1984年 | 387篇 |
1983年 | 338篇 |
1982年 | 308篇 |
1981年 | 299篇 |
1980年 | 265篇 |
1979年 | 260篇 |
1978年 | 266篇 |
1977年 | 245篇 |
1976年 | 244篇 |
1975年 | 290篇 |
1974年 | 215篇 |
1973年 | 208篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Comparative analysis of the cattle and human genomes: detection of ZOO-FISH and gene mapping-based chromosomal homologies 总被引:6,自引:0,他引:6
Comparative chromosome painting with individual human chromosome-specific libraries (CSLs) on cattle metaphase chromosomes
delineated 46 homologous chromosomal segments between the two species. Continuous arrangement of these segments on individual
cattle chromosomes demonstrates a nearly complete coverage of the bovine karyotype and shows physical boundaries of bovine
chromosomal segments homologous to individual human chromosomes. Alignment of the available comparative gene mapping data
with the homologous segments strongly supports the detected gross homologies between the karyotypes of the two species. In
addition to cattle, four human CSLs were hybridized to sheep metaphase chromosomes also, to further verify the known karyotype
homology within the Bovidae. Besides its application to karyotype evolution research, the comparative knowledge provides for
rapid expansion of the much needed Type I locus-based bovine gene map.
Received: 9 September 1995 / Accepted: 4 December 1995 相似文献
22.
23.
R H?kanson D Chen E Lindstr?m P Norlén M Bj?rkqvist D Lehto-Axtelius 《The Yale journal of biology and medicine》1998,71(3-4):163-171
The enterochromaffin-like (ECL) cells of the oxyntic mucosa (fundus) of the stomach produce, store and secrete histamine, chromogranin A-derived peptides such as pancreastatin, and an unanticipated but as yet unidentified peptide hormone. The cells are stimulated by gastrin and pituitary adenylate cyclase activating peptide and suppressed by somatostatin and galanin. Choline esters and histamine seem to be without effect on ECL cell secretion. The existence of a gastrin-ECL cell axis not only explains how gastrin stimulates acid secretion but also may help to explore the functional significance of the ECL cells with respect to the nature and bioactivity of its peptide hormone. From the results of studies of gastrectomized/fundectomized and gastrin-treated rats, it has been speculated that the anticipated ECL-cell peptide hormone acts on bone metabolism. 相似文献
24.
A bacterial clone carrying sequences coding for elongation factor EF-1 alpha from Artemia 总被引:2,自引:0,他引:2
A bacterial cDNA clone was identified carrying one third of the nucleotides coding for elongation factor EF-1 alpha from the brine shrimp Artemia. The sequence of codons corresponds with the known sequence of amino acids of EF-1 alpha in the region involved. 相似文献
25.
Adnan Cavka Bj?rn Alriksson Shaunita H. Rose Willem H. van Zyl Leif J. J?nsson 《Journal of industrial microbiology & biotechnology》2011,38(8):891-899
The possibility to utilize fiber sludge, waste fibers from pulp mills and lignocellulose-based biorefineries, for combined production of liquid biofuel and biocatalysts was investigated. Without pretreatment, fiber sludge was hydrolyzed enzymatically to monosaccharides, mainly glucose and xylose. In the first of two sequential fermentation steps, the fiber sludge hydrolysate was fermented to cellulosic ethanol with the yeast Saccharomyces cerevisiae. Although the final ethanol yields were similar, the ethanol productivity after 9.5?h was 3.3?g/l/h for the fiber sludge hydrolysate compared with only 2.2?g/l/h for a reference fermentation with similar sugar content. In the second fermentation step, the spent fiber sludge hydrolysate (the stillage obtained after distillation) was used as growth medium for recombinant Aspergillus niger expressing the xylanase-encoding Trichoderma reesei (Hypocrea jecorina) xyn2 gene. The xylanase activity obtained with the spent fiber sludge hydrolysate (8,500?nkat/ml) was higher than that obtained in a standard medium with similar monosaccharide content (1,400?nkat/ml). Analyses based on deglycosylation with N-glycosidase?F suggest that the main part of the recombinant xylanase was unglycosylated and had molecular mass of 20.7?kDa, while a minor part had N-linked glycosylation and molecular mass of 23.6?kDa. Chemical analyses of the growth medium showed that important carbon sources in the spent fiber sludge hydrolysate included xylose, small aliphatic acids, and oligosaccharides. The results show the potential of converting waste fiber sludge to liquid biofuel and enzymes as coproducts in lignocellulose-based biorefineries. 相似文献
26.
H. Wiksell V. Ekstrand C. Wadström G. Auer 《Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)》2009,25(3):128-132
A large and increasing number of women in the western world will at some point during their life be investigated morphologically for some type of breast lesion. Fine Needle Aspiration (FNA) is one morphological method which is considered to be the fastest, cheapest and the most patient-friendly approach. However, the frequency of conclusive samples using this method varies and is often too low, especially when performed by unexperienced operators. In this study we have developed and tested a new semi-automated instrument (“CytoTest”) designed for FNA which is intended to improve the efficacy of the technique by increasing the percentage of conclusive samples. A total of 443 consecutive aspiration procedures on palpable breast lesions were performed to compare this new “CytoTest” equipment with the standard protocol using the same type of needles. We conclude that by increasing the extent and frequency of the reciprocatory motions used by an experienced sampling operator as well as enhancing the ejection pressure, the cellular yield can be increased almost three folded compared to the standard protocol. For cases with high amounts of non-diagnostic material (such as blood or cystic fluid) which were discarded, up to four times more sample could be obtained. Furthermore, the frequency of sparse samples under 1 mg was halved with use of the “CytoTest”. 相似文献
27.
28.
29.
30.