全文获取类型
收费全文 | 5237篇 |
免费 | 570篇 |
国内免费 | 336篇 |
出版年
2023年 | 108篇 |
2022年 | 85篇 |
2021年 | 169篇 |
2020年 | 211篇 |
2019年 | 234篇 |
2018年 | 175篇 |
2017年 | 231篇 |
2016年 | 205篇 |
2015年 | 243篇 |
2014年 | 260篇 |
2013年 | 376篇 |
2012年 | 190篇 |
2011年 | 228篇 |
2010年 | 203篇 |
2009年 | 243篇 |
2008年 | 279篇 |
2007年 | 287篇 |
2006年 | 259篇 |
2005年 | 236篇 |
2004年 | 193篇 |
2003年 | 166篇 |
2002年 | 193篇 |
2001年 | 163篇 |
2000年 | 156篇 |
1999年 | 114篇 |
1998年 | 85篇 |
1997年 | 80篇 |
1996年 | 68篇 |
1995年 | 71篇 |
1994年 | 99篇 |
1993年 | 54篇 |
1992年 | 76篇 |
1991年 | 58篇 |
1990年 | 44篇 |
1989年 | 38篇 |
1988年 | 27篇 |
1987年 | 32篇 |
1986年 | 23篇 |
1985年 | 40篇 |
1984年 | 25篇 |
1983年 | 18篇 |
1982年 | 23篇 |
1981年 | 16篇 |
1980年 | 15篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 15篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有6143条查询结果,搜索用时 15 毫秒
1.
2.
Chrysophtharta bimaculata (Olivier) (Coleoptera: Chrysomelidae) is a major defoliator of regeneration eucalypt trees in Tasmania causing a significant reduction in height and diameter increment of trees which reduces wood volume per hectare. A study to conserve and enhance the efficiency of coccinellid species chieflyCleobora mellyi (Mulsant) (Coleoptera: Coccinellidae), and the cantharid,Chauliognathus pulchellus (Macleay) (Coleoptera: Cantharidae), for the biological control ofC. bimaculata was conducted in young regeneration forests in southern Tasmania from 1991–92. Cantharid adults and coccinellid adults and larvae feed onC. bimaculata eggs and, to a lesser extent, young larvae. The study found that coccinellids were more active throughout the egg and early (1st and 2nd) stage ofC. bimaculata. The cantharid, however was active only during the egg stage of the prey and then disappeared from the plantation. The coccinellids were therefore the most useful predators, but their population declined when the prey reached the 3rd and 4th stages. As shortage of food may account for this decline, supplementary food was provided in the form of sucrose sprays or sugar granules at a feeding station. This resulted in the retention of both predators and particularly the coccinellids and enhanced their efficacy. 相似文献
3.
Present and future needs for algae and algal products 总被引:1,自引:0,他引:1
A review of the present needs, mainly for production of phycocolloids and food condiments, is given. Supply and demand vary from balanced, in some, to disproportionate in other fields. World-wide shortage of agarophytes contrasts with huge, unexploited beds of brown seaweeds.In future, partly conflicting trends will decide the needs for algae and algal products. Growth in the human population, pollution, overexploitation of land and lack of freshwater will encourage use of seaweeds. Modern biotechnology will favour this development, but will also be a serious threat to industrial exploitation of seaweeds. Future uses of marine algae will be decisively influenced by the effort put into and the results coming out of seaweed research. 相似文献
4.
Sven Kurbel 《BioEssays : news and reviews in molecular, cellular and developmental biology》2020,42(10):2000056
This paper discusses possible mechanisms that might lead to misinterpretations of collected data and makes new evidence-based medicine (EBM) recommendations to oppose the previously accepted preventive measures, or treatment options. It is focused on the danger of the “red meat” consumption, and the question whether eating pungent food is good or bad for our health and finally whether the “bad luck” concept of getting several cancer types is valid or not. These three topics got and still have significant media attention. Several mechanisms are proposed as possible causes of these apparent conflicts. Some of them have already been recognized but sadly remained less known to medical readers and also to the general population. Also see the video abstract here https://youtu.be/owjoRXrNShA . 相似文献
5.
本文讨论了不同条件下苋菜红在银基汞膜电极上的伏安行为.发现在 pH=4时,苋菜红在-0,24V 处有很灵敏的检出信号,在此条件下,汞膜电极有良好的再现性和使用寿命;在10-100ppb 范围内,还原电流与浓度呈良好的线性关系. 相似文献
6.
Mean egg cluster size of Luehdorfia puziloi yessoensis varied among habitats. The mean egg cluster size tended to be large when abundance of the larval food leaves expressed as the fresh weight of leaves per unit area at a given habitat was high. Since this variation was observed among closely located study plots (butterflies can easily move between study plots), the egg cluster size variation among habitats is likely to be a result of flexible response by females to varying food abundance for larvae. 相似文献
7.
8.
N. N. Starkova E. P. Koroleva T. V. Rotanova 《Russian Journal of Bioorganic Chemistry》2000,26(2):71-84
Selective proteolysis is one of the mechanisms for the maintenance of cell homeostasis via rapid degradation of defective
polypeptides and certain short-lived regulatory proteins. In prokaryotic cells, high-molecular-mass oligomeric ATP-dependent
proteases are responsible for selective protein degradation. In eukaryotes, most polypeptides are attacked by the multicatalytic
26S proteasome, and the degradation of the majority of substrates involves their preliminary modification with the protein
ubiquitin. The proteins undergoing the selective proteolysis often contain specific degradation signals necessary for their
recognition by the corresponding proteases.
This article is dedicated to the 25th Anniversary of the journal Bioorganicheskaya Khimiya 相似文献
9.
We investigated the population dynamics of Copidodiaptomus numidicus (Copepoda: Calanoida) and Thermocyclops dybowskii (Copepoda: Cyclopoida) in Castelo-do-Bode Reservoir (Portugal). Both species in the reservoir were regulated mainly by food availability during the summers of 1993 and 1994. C. numidicus was always more abundant than T. dybowskii in the reservoir. C. numidicus produced two generations during the sampling period of both years whereas T. dybowskii produced two and three generations in 1993 and 1994, respectively. Because of high temperatures and low rainfall in 1994, the reservoir was more eutrophic than in 1993. Higher clutch size and a higher percentage of ovigerous females suggest that both species were benefiting from better feeding conditions in 1994. Despite this, population growth was reduced in 1994 relatively to 1993. Vertebrate predation and predation by copepods seem to have been minor factors in explaining this decline. However, the presence of Mesostoma sp. in the reservoir may have contributed to the reduction of both copepod populations during specific periods in 1994 although the calanoid was more affected than the cyclopoid by this predation. 相似文献
10.