全文获取类型
收费全文 | 27383篇 |
免费 | 2962篇 |
国内免费 | 16篇 |
专业分类
30361篇 |
出版年
2022年 | 253篇 |
2021年 | 511篇 |
2020年 | 283篇 |
2019年 | 376篇 |
2018年 | 455篇 |
2017年 | 390篇 |
2016年 | 586篇 |
2015年 | 1091篇 |
2014年 | 1077篇 |
2013年 | 1490篇 |
2012年 | 1845篇 |
2011年 | 1786篇 |
2010年 | 1117篇 |
2009年 | 1001篇 |
2008年 | 1451篇 |
2007年 | 1456篇 |
2006年 | 1359篇 |
2005年 | 1373篇 |
2004年 | 1338篇 |
2003年 | 1208篇 |
2002年 | 1240篇 |
2001年 | 390篇 |
2000年 | 324篇 |
1999年 | 406篇 |
1998年 | 368篇 |
1997年 | 255篇 |
1996年 | 236篇 |
1995年 | 237篇 |
1994年 | 223篇 |
1993年 | 244篇 |
1992年 | 292篇 |
1991年 | 268篇 |
1990年 | 270篇 |
1989年 | 300篇 |
1988年 | 274篇 |
1987年 | 249篇 |
1986年 | 225篇 |
1985年 | 217篇 |
1984年 | 232篇 |
1983年 | 218篇 |
1982年 | 256篇 |
1981年 | 252篇 |
1980年 | 181篇 |
1979年 | 193篇 |
1978年 | 190篇 |
1977年 | 164篇 |
1976年 | 163篇 |
1975年 | 163篇 |
1974年 | 155篇 |
1973年 | 135篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
HIF-1 expression in healing wounds: HIF-1alpha induction in primary inflammatory cells by TNF-alpha 总被引:12,自引:0,他引:12
3.
As part of systematic studies of the genus Porphyrain New Zealand, constituent sugar analyses of cell wall polysaccharidesin situ in dry thalli were found to yield data that weretaxonomically informative. Variation in constituent sugar levels betweenspecieswas sufficient in some cases to be useful in species differentiation. Thereproductive state of thallus regions had a significant impact on the levels ofconstituent sugars, whereas storage of dried thalli for eight months had noeffect. Three epiphytic taxa currently classified as species ofPorphyra appear to be incorrectly placed within the genus,as their constituent sugars and the levels of these sugars differed markedlyfrom those of all other species examined. 相似文献
4.
ABSTRACT The phrase persistent vulnerability reflects the enduring relationship of the rural population in Ceará with a highly variable climate. Persistence underscores the historical and unyielding nature of this vulnerability. Yet contrary to once-catastrophic rates of mortality etched in a public consciousness, no one dies from severe droughts and few people flee them as in the past. Government relief and social transfers have become the institutionalized form of adaptation, giving way to the counterintuitive reality that drought stabilizes the food and income supply for poor people. We analyze how maladaptive risk reduction, which is embedded in clientilistic social relations, undermines resilience, and we examine pathways toward a more sustainable adaptive relationship. 相似文献
5.
Maria V. Sergeeva Vadim V. Mozhaev Joseph O. Rich Yuri L. Khmelnitsky 《Biotechnology letters》2000,22(17):1419-1422
A novel biocatalytic reaction of transamidation of non-activated amides with amines is reported. Among 45 different lipolytic and proteolytic enzymes tested, only the lipase from Candida antarcticawas able to catalyze this reaction. The reaction proceeded with up to ca. 80% conversion in anhydrous methyl tert-butyl ether and worked with both N-substituted and unsubstituted amides. The biocatalytic transamidation is an equilibrium process and, therefore, higher conversions to the desired amide were achieved by using increased concentrations of the amine nucleophile. 相似文献
6.
David R. Nelson 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2013,368(1612)
The world we live in is a biosphere influenced by all organisms who inhabit it. It is also an ecology of genes, with some having rather startling effects. The premise put forth in this issue is cytochrome P450 is a significant player in the world around us. Life and the Earth itself would be visibly different and diminished without cytochrome P450s. The contributions to this issue range from evolution on the billion year scale to the colour of roses, from Darwin to Rachel Carson; all as seen through the lens of cytochrome P450. 相似文献
7.
Epithelial ovarian carcinoma (EOC), the major cause of gynaecological cancer death, is a heterogeneous disease classified into five subtypes. Each subtype has distinct clinical characteristics and is associated with different genetic risk factors and molecular events, but all are treated with surgery and platinum/taxane regimes. Tumour progression and chemoresistance is generally associated with major metabolic alterations, notably altered mitochondrial function(s). Here, we report for the first time that the expression of the mitochondrial regulators PGC1α and TFAM varies between EOC subtypes; furthermore, we have identified a profile in clear-cell carcinoma consisting of undetectability of PGC1α/TFAM, and low ERα/Ki-67. By contrast, high-grade serous carcinomas were characterised by a converse state of PGC1α/TFAM, ERα positivity and a high Ki-67 index. Interestingly, loss of PGC1α/TFAM and ERα was found also in a non-clear cell EOC cell line made highly resistant to platinum in vitro. Similar to clear-cell carcinomas, these resistant cells also showed accumulation of glycogen. Altogether, our data provide mechanistic insights into the chemoresistant nature of ovarian clear-cell carcinomas. Furthermore, these findings corroborate the need to take into account the diversity of EOC and to develop subtype specific treatment strategies. 相似文献
8.
9.
A Monte Carlo simulation of clone growth is discussed from the point of view of clonal volume. It is shown that clone volume is a good representation of the number of cells per clone for a wide range of single cell growth equations. However, the rate at which the coefficient of variation in clonal volume approaches that of cell number per clone is strongly dependent upon the particular growth equation. 相似文献
10.
Joseph V. Rodricks 《人类与生态风险评估》2014,20(1):3-28
The publication in 1962 of Rachel Carson's Silent Spring marks the mid-point in a century that saw, in its first half, the emergence of public health concerns related to human exposures to chemicals, and, in its second half, the emergence of public policies to deal with those concerns. Those policies made it imperative that the scientific community come to grips with the problem of identifying exposure levels not likely to cause harm. This problem was not significantly discussed within the scientific community until the 1950s, and well-described methods for practical solutions to it did not appear until the 1970s. An important report from the National Academy of Sciences, published in 1983 (Risk Assessment in the Federal Government), provided an analysis of these emerging methods, and recommended a useful framework for the assessment and management of risk. This framework remains central to public health and regulatory decision-making. A high-level perspective is offered on events leading to and following the 1983 report. The article describes early thinking about chemical toxicity and the scientific path that thinking followed through the 20th century, and to the present. 相似文献