全文获取类型
收费全文 | 20575篇 |
免费 | 1917篇 |
国内免费 | 13篇 |
专业分类
22505篇 |
出版年
2023年 | 121篇 |
2022年 | 300篇 |
2021年 | 568篇 |
2020年 | 266篇 |
2019年 | 389篇 |
2018年 | 435篇 |
2017年 | 341篇 |
2016年 | 590篇 |
2015年 | 989篇 |
2014年 | 1026篇 |
2013年 | 1405篇 |
2012年 | 1606篇 |
2011年 | 1581篇 |
2010年 | 976篇 |
2009年 | 846篇 |
2008年 | 1214篇 |
2007年 | 1202篇 |
2006年 | 1082篇 |
2005年 | 1021篇 |
2004年 | 921篇 |
2003年 | 856篇 |
2002年 | 827篇 |
2001年 | 203篇 |
2000年 | 155篇 |
1999年 | 183篇 |
1998年 | 171篇 |
1997年 | 142篇 |
1996年 | 120篇 |
1995年 | 111篇 |
1994年 | 118篇 |
1993年 | 116篇 |
1992年 | 126篇 |
1991年 | 120篇 |
1990年 | 102篇 |
1989年 | 93篇 |
1988年 | 99篇 |
1987年 | 81篇 |
1986年 | 71篇 |
1985年 | 97篇 |
1984年 | 99篇 |
1983年 | 66篇 |
1982年 | 81篇 |
1981年 | 73篇 |
1980年 | 68篇 |
1979年 | 78篇 |
1978年 | 57篇 |
1977年 | 61篇 |
1976年 | 65篇 |
1975年 | 72篇 |
1973年 | 58篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Selective Utilization of Pyrimidine Deoxyribonucleosides for Deoxyribonucleic Acid Synthesis in Pneumococcus 总被引:1,自引:1,他引:0 下载免费PDF全文
When pyrimidine deoxyribonucleosides are supplied to growing cultures of Diplococcus pneumoniae, they are selectively used for incorporation into deoxyribonucleic acid (DNA). Differently labeled molecules of deoxyuridine, thymidine, and deoxycytidine were used to study the precursor pathways of this organism. Each of these preformed pyrimidine deoxynucleosides is incorporated intact (i.e., without cleavage of the glycosidic bond) and is predominantly recoverable as DNA thymidine. During the utilization of deoxycytidine and deoxyuridine by pneumococci, large proportions of the available precursor are converted to free thymidine, which is secreted back into the growth medium. The biochemical pathways for selective incorporation into DNA and the regulation of concentrations of intracellular thymidine compounds by excretion of free thymidine are discussed. 相似文献
42.
Incomplete bacteriophage-like particles in ultraviolet-irradiated haemophilus 总被引:14,自引:10,他引:4 下载免费PDF全文
Incomplete phagelike particles were found in competent and incompetent cells of Haemophilus influenzae Rd (transformable) lysed after exposure to ultraviolet radiation. 相似文献
43.
D. G. McLarty W. D. Alexander R. McG. Harden D. H. Clark 《BMJ (Clinical research ed.)》1969,3(5664):200-203
Ninety patients who had a recurrence of thyrotoxicosis after thyroidectomy have been reviewed. All 10 patients who had a second operation and 18 out of 20 patients treated with a full course of antithyroid drugs relapsed. These results differ greatly from the results of treatment of the first episode of thyrotoxicosis, whether by thyroidectomy or antithyroid drugs. Radioiodine is the treatment of choice in this group of patients, despite the high incidence of hypothyroidism. 相似文献
44.
45.
46.
Assignment of the gene(s) involved in the expression of the proliferation-related Ki-67 antigen to human chromosome 10 总被引:2,自引:0,他引:2
D. M. Schonk H. J. H. Kuijpers E. van Drunen C. H. van Dalen A. H. M. Geurts van Kessel R. Verheijen F. C. S. Ramaekers 《Human genetics》1989,83(3):297-299
Summary The antigen recognized by the monoclonal antibody Ki-67 is a proliferation-related nucleolus-associated constituent used as a marker for cycling cells in tumor diagnosis. Antibody Ki-67 reacts with human proliferating cells, but not with hamster and mouse cells. Expression of the Ki-67 antigen was studied in a panel of human-rodent somatic cell hybrids. The results indicate that a gene involved in the expression of the antigen is located on chromosome 10. 相似文献
47.
Dorozynski A 《BMJ (Clinical research ed.)》1994,308(6940):1319-1320
48.
Dorozynski A 《BMJ (Clinical research ed.)》1994,308(6933):873-874
49.
Alexander A. DiIorio Pamela J. Weathers Ronald D. Cheetham 《Applied microbiology and biotechnology》1993,39(2):174-180
Transformed root tissue of Beta vulgaris (Detroit Dark Red) was permeabilized to stimulate the release of intracellularly stored betanin without adverse affects on tissue viability as measured by biomass accumulation. Product release of up to 15% (w/w) was achieved by heat treatment at 42°C for 45 min with minimal effect on viability. Higher levels of product release were obtained with increasing temperature and exposure, but at the expense of viability. Viability was measured by comparing dry weight increases of permeabilized tissue 3 days after treatment vs non-permeabilized tissue over the same time interval. Recovery of heat-treated tissue was improved by addition of CaCl2 (20 mm for 10 min) post-heat treatment. Betanin release up to 15% was also obtained at ambient temperature (25°C) by addition of up to 20 mm (NH4)2SO4 in the presence of 1 mm ethylenediaminetetraacetic acid (EDTA).
Correspondence to: A. A. DiIorio 相似文献
50.
This volume follows failures out into the world, exploring how they unfold ethnographically. Taking a longer view shows how objects, narratives, and diagnoses of failures may be crafted, acted on, suffered, resisted – unmade or recomposed. Thus while tropes and diagnoses of failure can temporarily (re)organize, narrate, and stabilize the world, the kinds of failures explored here also indicate a mode of uncontainable excess that refuses the boundedness of knowledge objects, temporalities, and spaces. This volume offers three main interventions. The first concerns knowledge production: how objects of failure are crafted through selective ways of knowing that occlude both other modes of apprehension at different scales and failure's many affective valences. The second thinks through the knotted temporalities – whether pasts, futures, suspended presents, or repetition and sedimentation – that make and are made by failure. Finally, writing about unfurling failures requires careful attention to non-linear reverberations and traces as well as to open-ended and mobile narratives that produce different social and material effects. 相似文献