全文获取类型
收费全文 | 15855篇 |
免费 | 1355篇 |
国内免费 | 12篇 |
专业分类
17222篇 |
出版年
2023年 | 84篇 |
2022年 | 213篇 |
2021年 | 390篇 |
2020年 | 209篇 |
2019年 | 247篇 |
2018年 | 337篇 |
2017年 | 256篇 |
2016年 | 446篇 |
2015年 | 675篇 |
2014年 | 750篇 |
2013年 | 899篇 |
2012年 | 1219篇 |
2011年 | 1217篇 |
2010年 | 770篇 |
2009年 | 696篇 |
2008年 | 986篇 |
2007年 | 978篇 |
2006年 | 944篇 |
2005年 | 816篇 |
2004年 | 786篇 |
2003年 | 756篇 |
2002年 | 681篇 |
2001年 | 219篇 |
2000年 | 168篇 |
1999年 | 220篇 |
1998年 | 200篇 |
1997年 | 139篇 |
1996年 | 128篇 |
1995年 | 86篇 |
1994年 | 93篇 |
1993年 | 102篇 |
1992年 | 86篇 |
1991年 | 92篇 |
1990年 | 79篇 |
1989年 | 96篇 |
1988年 | 68篇 |
1987年 | 54篇 |
1986年 | 60篇 |
1985年 | 80篇 |
1984年 | 65篇 |
1983年 | 53篇 |
1982年 | 50篇 |
1981年 | 50篇 |
1980年 | 52篇 |
1979年 | 45篇 |
1978年 | 39篇 |
1976年 | 33篇 |
1975年 | 34篇 |
1974年 | 40篇 |
1973年 | 34篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Summary Contact kairomones and oviposition in a host egg stimulated arrestment behaviour in Trichogramma evanescens, characterised by a reduction in walking speed and increased turning. Previous oviposition experience did not influence a parasitoid's response to contact kairomones, but successive encounters with kairomone patches resulted in parasitoids habituating to the contact chemical. Oviposition on a kairomone patch did not reverse this habituation effect. It was concluded that contact kairomones and host eggs will both contribute independently to the duration of a patch visit. The selection of patches by T. evanescens will depend on its response to kairomones. Results from this study indicate that the application of contact kairomones to field crops will not necessarily increase the probability of parasitoids finding hosts. 相似文献
52.
Salts of transition elements that alter the rate of sperm cell movement act at or near calcium-binding sites. After living bull sperm cells had been preincubated in VO43?, Ni2+, Zn2+, Mn2+, and also La3+, they were then fixed. Crisply defined organelles and the absence of particulate deposits in the morphological controls contrasted sharply with the treated specimens; the latter contained regions of increased electron density, the nature and distribution of which depended on the test substance, reflecting the differential affinities of the specific ions. La3+ formed fine dense areas, mainly at the exocytic surface of the plasma membrane. VO43? marks the cell surface but also left particulate densities within the cell. Ni2+ caused a nearly uniformly dense deposit at the surface and on the satellite fibers and axonemal microtubules. Zn2+ formed less uniform but coarser deposits, while in Mn2+ the distribution was similar to that in Zn2+ but much denser in the axonemal matrix and on the satellite fibers. Verapamil restricted the size and number of the opacities, while procaine permitted a similar distribution of slightly larger size reaction product. The differences in size and distribution of the enhanced densities were consistent and replicable for the individual assay substances. Vanadate, which specifically inhibits Na, K-ATPase, bound to ouabain-sensitive enzyme loci, however, completely disrupting the axonemal complex. This suggests that an important role of dynein in flagellar motion may relate to intracellular transport of Ca2+. 相似文献
53.
54.
Murray M. P.; Spurr G. B.; Sepic S. B.; Gardner G. M.; Mollinger L. A. 《Journal of applied physiology》1985,59(1):87-91
To identify the degree of difference between treadmill and floor walking, kinematic, electromyographic (EMG), and heart rate measurements were recorded in seven normal female subjects during walking at three speeds on the treadmill and on the floor. During treadmill walking, subjects tended to use a faster cadence and shorter stride length than during floor walking. In addition the displacements of the head, hip, and ankle in the sagittal plane showed statistically significant differences between floor and treadmill walking. Average EMG activity was usually greater on the treadmill than on the floor; however, this difference was only significant for the quadriceps. Heart rate was significantly higher during fast treadmill walking than floor walking. In general, treadmill walking was not found to differ markedly from floor walking in kinematic measurements or EMG patterns. 相似文献
55.
Ammonium release by zooplankton in suspensions of heat-killed algae and an evaluation of the flow-cell method 总被引:1,自引:0,他引:1
Vanderploeg Henry A.; Laird Gwenyth A.; Liebig James R.; Gardner Wayne S. 《Journal of plankton research》1986,8(2):341-352
The maximum excretion rate of NH4 (39 nmol mg dry wt1h1) was directly measured for Daphnia pulex by measuringNH4 accumulation in bottles containing D. pulex and dense, satiatingsuspensions of heat-killed algae. Ammonium release rates inthe algal suspensions were compared to those of individual animalsremoved from the suspension and placed in flow cells. Ammoniumrelease rate, R (nmol mg dry wt1 h1). in the flowcell decreased very rapidly with time, t (min), after removalaccording to the relation R = 26 + 25e0.16t. Ammoniumexcretion obtained by the flow cell method after extrapolationto time zero was not significantly different from that obtainedin the bottles. The considerable experiment-to-experiment variationin NH4 excretion was in large part correlated (r2 = 0.73) withthe feeding rate on the algae. 相似文献
56.
57.
Keisuke Kohmoto Kazuya Akimitsu Tetsuyuki Kohguchi Hiroshi Otani John M. Gardner 《Plant cell reports》1986,5(1):54-56
Amberlite XAD-7, a nonionic polyacrylate adsorbent, was found to be a very effective protectant for isolating mitochondria from tissues rich in oils and phenolics. Physiologically active, well-coupled mitochondria were successfully prepared from young green leaf tissues of citrus, apple, pear and tobacco.Abbreviations DNP
2,4-dinitrophenol
- CCCP
carbonyl cyanide m-chlorophenylhydrazone
- BSA
bovine serum albumin
- PVP
polyvinylpyrrolidone 相似文献
58.
59.
Tilletia indica teliospores were studied by use of thin sections and freeze-etch replicas. Surfaces of these spores have rodlet patterns which differ from those previously reported for spores of other fungi. The rodlets on T. indica teliospores average 240 nm in length and are not grouped into fascicles. 相似文献
60.
Some properties of monolayers of (POPG) alone or of POPG in mixtures with (DPPC) have been measured near 35°C during dynamic compression and expansion at 3.6 cm2·s?1. (2) The mean values of minimum surface tension (corresponding to maximum surface pressure) which could be obtained with pure POPG monolayers at high compression ranged from 15 to 18 mN·m?1 in the presence of Na+, Ca2+ or low pH (2.0) in the subphase. (3) The presence of Ca2+ or low pH in the subphase increased the collapse plateau ratios obtained on cyclic compression. This might represent enhanced respreading into the monolayer of pure POPG from a collapsed form during reexpansion of the surface. (4) Monolayers containing 10% or 30% POPG and 90% or 70% DPPC could be compressed to surface tensions approaching zero. (5) In such mixed monolayers, 10% or 30% POPG did not appear to enhance respreading, as measured by collapse plateau ratios, in the presence of Na+ or Ca2+ in the subphase. 相似文献