全文获取类型
收费全文 | 2833篇 |
免费 | 337篇 |
专业分类
3170篇 |
出版年
2021年 | 31篇 |
2020年 | 21篇 |
2019年 | 26篇 |
2018年 | 34篇 |
2017年 | 23篇 |
2016年 | 61篇 |
2015年 | 99篇 |
2014年 | 116篇 |
2013年 | 126篇 |
2012年 | 151篇 |
2011年 | 159篇 |
2010年 | 99篇 |
2009年 | 102篇 |
2008年 | 126篇 |
2007年 | 125篇 |
2006年 | 111篇 |
2005年 | 112篇 |
2004年 | 95篇 |
2003年 | 107篇 |
2002年 | 106篇 |
2001年 | 60篇 |
2000年 | 53篇 |
1999年 | 50篇 |
1998年 | 36篇 |
1997年 | 30篇 |
1996年 | 24篇 |
1995年 | 23篇 |
1994年 | 28篇 |
1992年 | 48篇 |
1991年 | 46篇 |
1990年 | 29篇 |
1989年 | 32篇 |
1988年 | 47篇 |
1987年 | 34篇 |
1986年 | 28篇 |
1985年 | 34篇 |
1984年 | 38篇 |
1983年 | 36篇 |
1982年 | 31篇 |
1981年 | 44篇 |
1980年 | 29篇 |
1979年 | 26篇 |
1977年 | 22篇 |
1976年 | 28篇 |
1974年 | 25篇 |
1973年 | 26篇 |
1971年 | 20篇 |
1970年 | 21篇 |
1969年 | 26篇 |
1968年 | 25篇 |
排序方式: 共有3170条查询结果,搜索用时 15 毫秒
1.
Stephen B. Vander Wall 《Animal behaviour》1982,30(1):84-94
Five hypotheses of cache recovery behaviour in Clark's nutcracker (Nucifraga columbiana) were examined experimentally. Most caches were made in soil within 5 cm of conspicuous large objects. Both seed-caching and non-seed-caching nutcrackers were able to locate caches. Seed-caching nutcrackers relocated caches using large objects as remembered visual cues. Soil microtopography and small (<2 cm diameter) objects may be used as cues to facilitate cache recovery but are not essential. Non-seed-caching nutcrackers located caches by using soil disturbances at cache sites as visual cues and by searching preferentially near objects where caches were concentrated. Success rates of seed-caching nutcrackers ranged from 52 to 78% and those of non-seed-caching nutcrackers ranged from 8 to 12%. Nutcrackers do not use random search or olfactory cues to locate caches. 相似文献
2.
3.
4.
5.
Dorothy Trainor 《CMAJ》1982,126(10):1235-1237
6.
P. Angell W.J. Machowski P.P. Paul C.M. Wall F.F. Lyle Jr. 《Journal of microbiological methods》1997,30(3):173-178
A multiple chemostat system has been developed in which metal specimens can be exposed to a consortium of bacteria. The system comprises a single test chemostat containing the test specimen operated at a high dilution rate to facilitate the wash out of planktonic bacteria, selecting for attached or biofilm growth. This chemostat is fed at a steady low rate by a number of separate chemostats each of which contains a pure axenic culture of one member of the consortium being tested. This system has the advantage of providing a continual inoculum of the test species to the test specimen allowing both aerobic and anaerobic bacteria to be grown in the same system. Constant levels of three bacterial types were maintained in the system: Pseudomonas aeruginosa, Thiobacillus ferrooxidans and Desulfovibrio vulgaris. Exposure of 316L stainless steel electrodes to this system resulted in increased corrosion of coupons exposed biotically, as compared to those exposed abiotically. A current monitoring technique and electrochemical impedance spectroscopy were used to evaluate effects of bacteria on metallic corrosion. 相似文献
7.
The 13C NMR spectra of geosmin, selina-4(14),7(11)-diene-99-ol and two dihydroeudesmol isomers have been obtained and the individual resonances assigned. Several different empirical correlations developed by others have been combined in simple calculations to predict chemical shift values for sesquiterpenols of the eudesmane group. 相似文献
8.
9.
10.