全文获取类型
收费全文 | 5017篇 |
免费 | 494篇 |
国内免费 | 1篇 |
专业分类
5512篇 |
出版年
2023年 | 25篇 |
2022年 | 77篇 |
2021年 | 134篇 |
2020年 | 76篇 |
2019年 | 87篇 |
2018年 | 112篇 |
2017年 | 75篇 |
2016年 | 161篇 |
2015年 | 236篇 |
2014年 | 286篇 |
2013年 | 295篇 |
2012年 | 389篇 |
2011年 | 373篇 |
2010年 | 227篇 |
2009年 | 186篇 |
2008年 | 246篇 |
2007年 | 253篇 |
2006年 | 202篇 |
2005年 | 216篇 |
2004年 | 203篇 |
2003年 | 174篇 |
2002年 | 146篇 |
2001年 | 74篇 |
2000年 | 73篇 |
1999年 | 52篇 |
1998年 | 60篇 |
1997年 | 48篇 |
1996年 | 37篇 |
1995年 | 42篇 |
1994年 | 42篇 |
1993年 | 37篇 |
1992年 | 64篇 |
1991年 | 36篇 |
1990年 | 40篇 |
1989年 | 43篇 |
1988年 | 35篇 |
1987年 | 34篇 |
1986年 | 31篇 |
1985年 | 38篇 |
1984年 | 32篇 |
1983年 | 27篇 |
1982年 | 24篇 |
1981年 | 30篇 |
1980年 | 32篇 |
1979年 | 26篇 |
1978年 | 34篇 |
1977年 | 26篇 |
1976年 | 27篇 |
1975年 | 30篇 |
1974年 | 24篇 |
排序方式: 共有5512条查询结果,搜索用时 0 毫秒
21.
22.
The first call for applications to the NHS research and development programme on the interface between primary and secondary care was advertised in February 1994. A total of 674 outline proposals were submitted and 54 (8%) secured funding. Projects have been commissioned in 16 of the 21 priority areas and around 6m pounds has been committed. Analysis shows that multidisciplinary applications are more likely to be funded and that the odds for a successful application are on average nearly doubled for each discipline represented up to five. A survey of applicants and peer reviewers found satisfaction with much of the commissioning process, but peer review and feedback were subject to criticism, particularly by unsuccessful applicants. The programme shows that it is possible to commission a large number of projects in an innovative area of research and development and has identified refinements that will further increase the efficiency and acceptability of the process. 相似文献
23.
Neal R. Spencer 《Economic botany》1984,38(4):407-416
Velvetleaf,Abutilon theophrasti, a native of China, was originally introduced into the New World before 1750 as a potential fiber crop for the American colonies. Initial introductions may have come from England because of similar interests in the development of fiber crops. Commercial fiber production from velvetleaf was attempted by U.S. farmers for more than a century. The latest known attempts were made in the latter part of the 19th century in Illinois and New York. Velvetleaf never competed well with hemp, at least partly due to a lack of proper machinery for fiber processing. These early experimental plantings were apparently the source of velvetleaf as a weed in row crops. One velvetleaf plant is capable of producing as many as 8,000 seeds, and viability may extend beyond 50 yr. The plant is well adapted to our upper Midwest where maize (Zea mays) and soybeans (Glycine max) are the major row crops. The reservoir of velvetleaf seed in the soil is increasing. The current annual economic loss due to velvetleaf in maize and soybeans is estimated to be approximately $343 million per year. 相似文献
24.
Association with sludge solids did not allow poliovirus to enter cells other than through the normal receptor-mediated route. This implies that the infectivities of sludge-encapsulated virions are masked until their exposure permits binding to cell surface receptors. 相似文献
25.
26.
The bactericidal and opsonic activity of fresh human serum (FHS) for a mucoid strain ofPseudomonas aeruginosa, 144M, and its spontaneous nonmucoid revertant, 144NM, was examined. Strain 144M was sensitive to the bactericidal activity of FHS, but strain 144NM was not. This bactericidal activity was due to the combined interaction of IgG and IgM with complement, activated through both pathways. Neither 144M nor 144NM was ingested by human polymorphonuclear leukocytes (PMNL) without FHS. Whereas maximal phagocytosis of 144M required only 5% FHS, comparable ingestion of 144NM required 25% FHS. Maximal phagocytosis of either 144M or 144NM required IgG, IgM, and complement. However, 144M required a heat-sensitive opsonic IgG, whereas 144NM required a heat-resistant IgG. Using selective absorption techniques, the targets for bactericidal and opsonic immunoglobulins on 144M and 144NM appeared to be different, suggesting that the variant 144NM had one or more altered, absent, or inaccessible cell surface components that account for differences in response to FHS and PMNL. 相似文献
27.
Design optimization of continuous sterilizers 总被引:1,自引:0,他引:1
The development of a design of a continuous sterilization is considered with regard to practical data for temperature/time thermal deactivation of infecting organisms. An example of the optimization of the engineering design for capital and operating costs is given. Systems for continuous sterilization by membrane filtration are also considered. 相似文献
28.
29.
Phosphorylation on tyrosine-15 of p34(Cdc2) by ErbB2 inhibits p34(Cdc2) activation and is involved in resistance to taxol-induced apoptosis 总被引:4,自引:0,他引:4
Tan M Jing T Lan KH Neal CL Li P Lee S Fang D Nagata Y Liu J Arlinghaus R Hung MC Yu D 《Molecular cell》2002,9(5):993-1004
ErbB2 overexpression confers resistance to taxol-induced apoptosis by inhibiting p34(Cdc2) activation. One mechanism is via ErbB2-mediated upregulation of p21(Cip1), which inhibits Cdc2. Here, we report that the inhibitory phosphorylation on Cdc2 tyrosine (Y)15 (Cdc2-Y15-p) is elevated in ErbB2-overexpressing breast cancer cells and primary tumors. ErbB2 binds to and colocalizes with cyclin B-Cdc2 complexes and phosphorylates Cdc2-Y15. The ErbB2 kinase domain is sufficient to directly phosphorylate Cdc2-Y15. Increased Cdc2-Y15-p in ErbB2-overexpressing cells corresponds with delayed M phase entry. Expressing a nonphosphorylatable mutant of Cdc2 renders cells more sensitive to taxol-induced apoptosis. Thus, ErbB2 membrane RTK can confer resistance to taxol-induced apoptosis by directly phosphorylating Cdc2. 相似文献
30.
Tsihlis ND Oustwani CS Vavra AK Jiang Q Keefer LK Kibbe MR 《Cell biochemistry and biophysics》2011,60(1-2):89-97
Nitric oxide (NO) limits formation of neointimal hyperplasia in animal models of arterial injury in large part by inhibiting vascular smooth muscle cell (VSMC) proliferation through cell cycle arrest. The ubiquitin-conjugating enzyme UbcH10 is responsible for ubiquitinating cell cycle proteins for proper exit from mitosis. We hypothesize that NO prevents VSMC proliferation, and hence neointimal hyperplasia, by decreasing levels of UbcH10. Western blotting and immunofluorescent staining showed that NO reduced UbcH10 levels in a concentration-dependent manner in VSMC harvested from the abdominal aortas of Sprague-Dawley rats. Treatment with NO or siRNA to UbcH10 decreased both UbcH10 levels and VSMC proliferation (P<0.001), while increasing UbcH10 levels by plasmid transfection or angiotensin II stimulation increased VSMC proliferation to 150% (P=0.008) and 212% (P=0.002) of control, respectively. Immunofluorescent staining of balloon-injured rat carotid arteries showed a ~4-fold increase in UbcH10 levels, which was profoundly decreased following treatment with NO. Western blotting of carotid artery lysates showed no UbcH10 in uninjured vessels, a substantial increase in the injury alone group, and a significant decrease in the injury+NO group (~3-fold reduction versus injury alone). Importantly, in vitro and in vivo, a marked increase in polyubiquitinated UbcH10 was observed in the NO-treated VSMC and carotid arteries, respectively, indicating that NO may be decreasing unmodified UbcH10 levels by increasing its ubiquitination. Central to our hypothesis, we report that NO decreases UbcH10 levels in VSMC in vitro and following arterial injury in vivo in association with increasing polyubiquitinated-UbcH10 levels. These changes in UbcH10 levels correlate with VSMC proliferation and neointimal hyperplasia, making UbcH10 a promising therapeutic target for inhibiting this proliferative disease. 相似文献