全文获取类型
收费全文 | 31119篇 |
免费 | 2620篇 |
国内免费 | 3688篇 |
出版年
2024年 | 121篇 |
2023年 | 683篇 |
2022年 | 815篇 |
2021年 | 985篇 |
2020年 | 1063篇 |
2019年 | 1408篇 |
2018年 | 1099篇 |
2017年 | 1161篇 |
2016年 | 1211篇 |
2015年 | 1289篇 |
2014年 | 1649篇 |
2013年 | 2212篇 |
2012年 | 1262篇 |
2011年 | 1504篇 |
2010年 | 1231篇 |
2009年 | 1611篇 |
2008年 | 1681篇 |
2007年 | 1662篇 |
2006年 | 1547篇 |
2005年 | 1431篇 |
2004年 | 1277篇 |
2003年 | 1131篇 |
2002年 | 1028篇 |
2001年 | 811篇 |
2000年 | 696篇 |
1999年 | 748篇 |
1998年 | 586篇 |
1997年 | 546篇 |
1996年 | 500篇 |
1995年 | 500篇 |
1994年 | 485篇 |
1993年 | 372篇 |
1992年 | 348篇 |
1991年 | 338篇 |
1990年 | 268篇 |
1989年 | 249篇 |
1988年 | 227篇 |
1987年 | 210篇 |
1986年 | 168篇 |
1985年 | 195篇 |
1984年 | 204篇 |
1983年 | 140篇 |
1982年 | 168篇 |
1981年 | 117篇 |
1980年 | 119篇 |
1979年 | 103篇 |
1978年 | 81篇 |
1977年 | 45篇 |
1976年 | 40篇 |
1974年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Aspects Affecting Biosynthesis and Biotransformation of Secondary Metabolites in Plant Cell Cultures
《Critical reviews in biotechnology》2013,33(2):105-118
AbstractBiosensors are useful analytical devices that can be integrated with on-line process monitoring schemes. In this article, the principles and applications of these devices for bioprocess monitoring are considered. Several different types of biosensors are described, and the applications and limitations of flow injection analysis (FIA) for these applications are discussed. It is hoped that the background provided here can be useful to researchers in this area. 相似文献
62.
P. Loslever J. Schiro F. Gabrielli P. Pudlo 《Computer methods in biomechanics and biomedical engineering》2017,20(10):1038-1047
The purpose of this article is to compare Principal Component Analysis (PCA) and a much less used method, i.e. MCA (Multiple Correspondence Analysis) with data being first changed into membership values to fuzzy space windows. For such a comparison, data from an experimental study about turning the steering wheel is used. In a didactic perspective, this article only considers one multidimensional signal with 5 components: 3 linked to the steering wheel angle and hand positions and 2 to hand effort variables. A discussion weighs out the pros and the cons of both methods with criteria such as the possibility to show complex relational phenomena, the analysis/computing time or the information loss inherent to the averaging stage (in the perspective to analyze several hundreds of large multidimensional signals). 相似文献
63.
64.
X. Y. Li C. M. Han Y. Wang H. Z. Liu Z. F. Wu Q. H. Gao S. H. Zhao 《Animal genetics》2010,41(5):537-540
RIG-1 signalling is responsible for the detection of cytoplasmic viral RNA molecules. DEXH (Asp-Glu-X-His) box polypeptide 58 (encoded by DHX58) is a negative regulator of the RIG-1 signalling pathway. In human, the DHX58 gene can be upregulated and can inhibit the RIG-1 signalling pathway during viral infection. In this study, porcine DHX58 gene expression patterns were studied. According to our results, the porcine DHX58 gene was upregulated not only by the stimulation of Poly I:C but also by the stimulation of 1ipopolysaccharides (LPS). One polymorphism (g.4919G>C), detected in the ninth intron, was significantly associated with some blood parameters including the red cell distribution width of 1-day-old pigs and white blood cell counts, lymphocyte absolute counts, and platelet distribution width of 17-day-old pigs (P < 0.05). Moreover, the individuals with the genotype GG have a significantly higher mean white blood cell count than individuals with genotype CC or GC (P < 0.05). Our study indicates that DHX58 is an important gene that is associated with the immune response in swine. 相似文献
65.
The measurement of the ATP content of fresh semen is as accurate as the estimation of sperm motility by conventional methods in discriminating between semen of fertile versus subfertile men. The ATP content of frozen thawed donor semen is correlated with the probability of conception per cycle of insemination. Exact quantification of cytotoxic sperm antibodies in serum is possible with the adenosine-triphosphate-release-cytotoxicity test, since measurement is free of the bias of microscopic examination. The procedure has been simplified by testing only one serum dilution and calculating the ‘sperm toxicity index’. 相似文献
66.
L. Brzsnyi 《Biometrical journal. Biometrische Zeitschrift》1981,23(3):283-295
The paper deals with the analysis of 2 × 2 table measures and describes several new possibilities for applying them. An estimate is given for HELLMICH's asymmetric K-measure and a possible extension of the contingency concept in a special 2×2 case is presented. The concept introduced and the recommended computer application of the 2×2 table measures is supported by new results obtained for the relationship between jaw joint pains and noises examined earlier by F. SCHMID and C. ZSCHEGE. With a larger number of observations the opportunity arises for a deeper analysis of this dental problem using path analysis. The plan of evaluation and the conncetion between the variables examined is illustrated by a path-diagram. The association tables determined on the basis of the (C) values introduced during the examination of jaw joint disturbances using association analysis draw attention to the special role of the left side of mastication. The paper raises ideas for further generalisations and indicates where further research is needed. 相似文献
67.
68.
69.
Summary We report on the size distribution of clones marked by mitotic recombination induced by several different doses of X-rays applied to 72 h oldDrosophila larvae. The results indicate that the radiation significantly reduces the number of cells which undergo normal proliferation in the imaginal wing disc. We estimate that 1000 r reduces by 40–60% the number of cells capable of making a normal contribution to the development of the adult wing. Part of this reduction is due to severe curtailment in the proliferative ability of cells which nevertheless remain capable of adult differentiation; this effect is possibly due to radiation-induced aneuploidy. Cytological evidence suggests that immediate cell death also occurs as a result of radiation doses as low as 100 r. The surviving cells are stimulated to undergo additional proliferation in response to the X-ray damage so that the result is the differentiation of a normal wing. 相似文献
70.
Coral reefs are generally considered to be the most biologically productive of all marine ecosystems, but in recent times these vulnerable aquatic resources have been subject to unusual degradation. The general decline in reefs has been greatly accelerated by mass bleaching in which corals whiten en masse and often fail to recover. Empirical evidence indicates a coral reef bleaching cycle in which major bleaching episodes are synchronized with El Niño events that occur every 3–4 years on average. By heating vast areas of the Pacific Ocean, and affecting the Indian and Atlantic Oceans as well, El Niño causes widespread damage to reefs largely because corals are very sensitive to temperature changes. However, mass bleaching events were rarely observed before the 1970s and their abrupt appearance two decades ago remains an enigma. Here we propose a new explanation for the sudden occurrence of mass bleaching and show that it may be a response to the relative increase in El Niño experienced over the last two decades. 相似文献