全文获取类型
收费全文 | 7629篇 |
免费 | 864篇 |
国内免费 | 3篇 |
专业分类
8496篇 |
出版年
2022年 | 52篇 |
2021年 | 106篇 |
2020年 | 62篇 |
2019年 | 87篇 |
2018年 | 106篇 |
2017年 | 97篇 |
2016年 | 172篇 |
2015年 | 327篇 |
2014年 | 331篇 |
2013年 | 344篇 |
2012年 | 558篇 |
2011年 | 524篇 |
2010年 | 322篇 |
2009年 | 312篇 |
2008年 | 417篇 |
2007年 | 382篇 |
2006年 | 332篇 |
2005年 | 343篇 |
2004年 | 335篇 |
2003年 | 327篇 |
2002年 | 304篇 |
2001年 | 125篇 |
2000年 | 117篇 |
1999年 | 135篇 |
1998年 | 106篇 |
1997年 | 81篇 |
1996年 | 79篇 |
1995年 | 77篇 |
1994年 | 72篇 |
1993年 | 60篇 |
1992年 | 95篇 |
1991年 | 75篇 |
1990年 | 89篇 |
1989年 | 95篇 |
1988年 | 91篇 |
1987年 | 97篇 |
1986年 | 70篇 |
1985年 | 83篇 |
1984年 | 71篇 |
1983年 | 72篇 |
1982年 | 61篇 |
1981年 | 54篇 |
1979年 | 78篇 |
1978年 | 79篇 |
1977年 | 56篇 |
1976年 | 46篇 |
1975年 | 48篇 |
1974年 | 54篇 |
1973年 | 58篇 |
1972年 | 50篇 |
排序方式: 共有8496条查询结果,搜索用时 0 毫秒
1.
2.
3.
The risk of malignancy in large congenital nevi 总被引:4,自引:0,他引:4
E N Kaplan 《Plastic and reconstructive surgery》1974,53(4):421-428
4.
Pollen isolated from cold treated and precultivated anthers of tobacco (Nicotiana tabacum L. var. Wisconsin 38) were separated into different fractions with counter-current distribution using an aqueous Dextran-polyethylene glycol two-phase system. It was possible to distinguish among eight pollen classes differing in developmental stage and in partitioning. A part of each fraction was cultivated for analysis of embryo formation. This was highest in a fraction with an intermediate to high partition in the phase system. Enriched in this fraction were also pollen that were fairly well stained with acetocarmine, contained several nuclei and had a relatively low mitochondrial activity. The enrichment of embryogenic pollen offers several advantages especially to physiological studies on embryogenesis. 相似文献
5.
Dana M. Bergstrom George R. Stewart Patricia M. Selkirk Susanne Schmidt 《Oecologia》2002,130(2):309-314
'15N signatures of fossil peat were used to interpret past ecosystem processes on tectonically active subantarctic Macquarie Island. By comparing past vegetation reconstructed from the fossil record with present-day vegetation analogues, our evidence strongly suggests that changes in the '15N signatures of fossil peat at this location reflect mainly past changes in the proportion of plant nitrogen derived from animal sources. Associated with uplift above sea level over the past 8,500 years, fossil records in two peat deposits on the island chronicle a change from coastal vegetation with fur and elephant seal disturbance to the existing inland herbfield. Coupled with this change are synchronous changes in the '15N signatures of peat layers. At two sites 15N-enriched peat '15N signatures of up to +17 were associated with a high abundance of pollen of the nitrophile Callitriche antarctica (Callitrichaceae). At one site fossil seal hair was also associated with enriched peat '15N. Less 15N enriched '15N signatures (e.g. -1.9 to +3.9) were measured in peat layers which lacked animal associated C. antarctica and Acaena spp. Interpretation of a third peat profile indicates continual occupation of a ridge site by burrowing petrels for most of the Holocene. We suggest that 15N signatures of fossil peat remained relatively stable with time once deposited, providing a significant new tool for interpreting the palaeoecology. 相似文献
7.
Regulatory volume decrease in alveolar macrophages: cation loss is not correlated with changes in membrane recycling 总被引:2,自引:0,他引:2
Alveolar macrophages regain their normal volume after swelling in hypo-osmotic solutions. This process, termed regulatory volume decrease (RVD), is initiated 3-5 minutes after exposure of cells to hypo-osmotic solutions, and by 30 min, near-normal volumes are attained. Volume decrease does not occur at 0 degrees C or in solutions in which Na+ has been replaced by K+, or Cl- by the impermeant anion gluconate. These results, as well as direct measurement of intracellular cations, indicate that decreases in cell volume result primarily from the loss of K+ and Cl- and are similar to RVD in lymphocytes. Kinetic analysis of cation loss, both by directly measuring changes in intracellular cation content and by assaying rubidium efflux, showed that cation loss occurred immediately upon media dilution. The rate of cation loss fit first-order kinetics and preceded both the initiation of volume decrease and the maximum increase in surface receptor number. These results suggest that the cation transporters responsible for RVD are located at the cell surface and that regulation of activity is not dependent on alterations in membrane movement. 相似文献
8.
The first seven amino acids encoded by the v-src oncogene act as a myristylation signal: lysine 7 is a critical determinant. 总被引:44,自引:14,他引:30
The transforming protein of Rous sarcoma virus, pp60v-src, is covalently coupled to myristic acid by an amide linkage to glycine 2. Myristylation promotes the association of pp60v-src with cellular membranes, and this subcellular location is essential for transforming activity. The findings presented here, in conjunction with the previous reports of others, imply that the seventh amino acid encoded by v-src might be important in the myristylation reaction. Replacement of lysine 7 by asparagine greatly reduced the myristylation, membrane association, and transforming activity of pp60v-src. In contrast, substitution of arginine at residue 7 had no effect on any of these properties of pp60v-src. Addition of amino acids 1 to 7 encoded by v-src was sufficient to cause myristylation of a src-pyruvate kinase fusion protein. We conclude that the recognition sequence for myristylation of pp60v-src comprises amino acids 1 to 7 and that lysine 7 is a critical component of this sequence. 相似文献
9.
Light-dependent regulation of the synthesis of soluble and intracytoplasmic membrane proteins of Rhodopseudomonas sphaeroides. 总被引:15,自引:13,他引:2 下载免费PDF全文
Cells of Rhodopseudomonas sphaeroides grown under saturating light conditions (30 W/m2) and then shifted to low light intensity (3 W/m2) required 2.5 h to adapt to the new lower light conditions. After the shift, cell growth, whole cell protein accumulation, and bacteriochlorophyll accumulation ceased immediately. Approximately midway into the adaptation period, bacteriochlorophyll synthesis commenced at a new, higher rate, which continued through the beginning of the low-light growth period until new steady-state levels were reached. Immediately after the downshift, the rate of cellular protein synthesis declined to 22% of its preshift rate. Pulse-labeling of protein throughout the adaptation period and comparison with a steady-state prelabel culture revealed that synthesis of two of the three light-harvesting proteins, as well as two additional high-molecular-weight photosynthetic membrane proteins, was derepressed three- to fivefold compared with bulk cellular protein. Finally, the synthesis of at least three soluble proteins showed light-dependent regulation after the light downshift. These results are discussed in terms of the light-dependent regulation of synthesis of the photosynthetic membrane macromolecular components and the division of protein synthesis between the photosynthetic membranes and the soluble cell phase. 相似文献
10.