全文获取类型
收费全文 | 901篇 |
免费 | 63篇 |
国内免费 | 139篇 |
出版年
2023年 | 13篇 |
2022年 | 10篇 |
2021年 | 14篇 |
2020年 | 19篇 |
2019年 | 33篇 |
2018年 | 39篇 |
2017年 | 42篇 |
2016年 | 47篇 |
2015年 | 29篇 |
2014年 | 45篇 |
2013年 | 53篇 |
2012年 | 32篇 |
2011年 | 34篇 |
2010年 | 28篇 |
2009年 | 42篇 |
2008年 | 49篇 |
2007年 | 51篇 |
2006年 | 47篇 |
2005年 | 34篇 |
2004年 | 36篇 |
2003年 | 31篇 |
2002年 | 27篇 |
2001年 | 28篇 |
2000年 | 23篇 |
1999年 | 19篇 |
1998年 | 12篇 |
1997年 | 19篇 |
1996年 | 21篇 |
1995年 | 31篇 |
1994年 | 14篇 |
1993年 | 14篇 |
1992年 | 15篇 |
1991年 | 15篇 |
1990年 | 11篇 |
1989年 | 14篇 |
1988年 | 13篇 |
1987年 | 5篇 |
1986年 | 8篇 |
1985年 | 11篇 |
1984年 | 16篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1981年 | 8篇 |
1980年 | 11篇 |
1979年 | 3篇 |
1978年 | 5篇 |
1977年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1970年 | 2篇 |
排序方式: 共有1103条查询结果,搜索用时 31 毫秒
1.
Summary In comparison to cassava grown in monoculture the root infection of cassava with vesicular-arbuscular mycorrhiza was increased by crop rotation with grain legumes in the field. This was also found when cassava was intercropped with legumes and fertilized. A possible specificity of mycorrhizal fungi to increase the yield of one species more than the other when grown in association, is discussed. 相似文献
2.
3.
Esteban E. Sarmiento 《International journal of primatology》1988,9(4):281-345
Observations on the behavior of living hominoids show generic differences in the use and posture of the wrist joint. Both
orang-utans and hylobatids usually use the wrist in suspensory behaviors. However, orang-utans emphasize markedly adducted
and flexed wrist postures, while hylobatids emphasize violent forearm and wrist rotation. African apes, especially the gorilla,
use the wrist more frequently than other hominoids for terrestrial quadrupedal weight-bearing. Humans use the wrist less frequently
for supportive purposes than do other hominoids. These behavioral differences correspond to structural specializations in
the proximal carpal joint of each of the hominoid genera. Although each of the hominoid genera has apparently modified its
proximal carpal joint best to serve its characteristic behaviors, all hominoids share a unique proximal carpal joint that
permits approximately 160ℴ of forearm rotation. The hylobatid proximal carpal joint is specialized in exhibiting a marked
development of those structures limiting forearm rotation, but it is in most respects the least derived— that is, closest
to the nonhominoid anthropoids. Chimpanzees show a proximal carpal joint that is more generalized than those of the other
great apes but more derived than that of hylobatids. The human and gorilla proximal wrist joints, on the other hand, show
marked modifications for weight-bearing in terrestrial behaviors. Orang-utans have the most derived proximal carpal joint,
which in many respects parallels that of the slow-climbing nonhominoid primates. The comparative anatomy and structural specializations
of the wrist joint support (a) an early divergence of hylobatids from the common hominoid stock, (b) a common ancestry for
gorillas and humans separate from the other hominoids, and (c) a long independent evolutionary period for orang-utans since
their divergence from the common hominoid stock, or one that was marked by strong selection pressures for wrist specializations.
Unfortunately, the generalized condition of the chimpanzee’s wrist joint and the very derived condition of the orang-utan
wrist provide uncertain evidence as to which of the two was first to diverge from the common hominoid stock. Identification
of hominoid wrist specializations as reflecting real phylogenetic relationships or parallelisms depends on how well the phytogeny
inferred from wrist morphology accords with those arrived at from the study of other systems. 相似文献
4.
R. Chima Wokocha 《Plant and Soil》1988,106(1):146-148
Populations of viable sclerotia ofSclerotium rolfsii were highest in soil in a field in which tomato was planted for three successive years before sampling and in one in which
tomato followed groundnut in the 2 years prior to this study. The lowest sclerotial numbers were recorded in fields in which
groundnut followed maize or in which maize or sorghum was the last crop before sampling. 相似文献
5.
Susanna T. Y. Tong 《Plant Ecology》1988,79(1-2):65-74
The plant-environment relationships in a range of matorral communities, having different rainfall conditions in semi-arid lowland habitats in Murcía, S.E. Spain, were examined using the non-metric multidimensional scaling ordination technique. Hypotheses on floristic variations were derived based on an interpretative strategy which involved a site configuration rotation, followed by stepwise multiple regression analysis. An environmental data set was used to isolate variables associated with site co-ordinate trends. Results showed that floristic variation in these communities was mainly determined by aspect induced radiation receipt. Besides, most environmental trends in the study areas were found to be oblique to original site ordination axes and configuration rotation seemed to be a prerequisite in quantitative interpretation. The interpretative strategy introduced in this study was effective. It enhanced straightforward, quantitative and objective interpretation whereby inductive inferences on environmental trends could be readily formulated.Abbreviations ARAD
radiation receipt surrogate
- DEPTH
soil depth
- DISTURB
disturbance index
- NMDS
non-metric multidimensional scaling
- NUT
nutrient scalar
- SLOPE
slope angle
- TEXTIN
texture index 相似文献
6.
7.
Richard E. Williamson 《Planta》1985,163(1):1-8
The mechanism by which sub-cortical actin bundles and membranous organelles are immobilised in the cortical cytoplasm of the alga Chara was studied by perfusing cells with a solution containing 1% Triton X-100. Light and scanning electron microscopy and the release of starch grains and chlorophyll-protein complexes indicated that the detergent extensively solubilised the chloroplasts. However, the sub-cortical actin bundles remained in situ even though they were originally separated from the plasma membrane by the chloroplasts. A fibrous layer between chloroplasts and plasma membrane became readily visible after detergent extraction of the cells and could be released by low-ionic-strength ethylenediaminetetraacetic acid, thioglycollate and trypsin. The same treatments applied to cells not subject to detergent extraction released the membrane-bound organelles and actin bundles and no fibrous meshwork was visible on subsequent extraction with Triton. It is, therefore, concluded that a detergent-insoluble cortical cytoskeleton exists and contributes to the immobility of the actin and cortical organelles in the cells.Abbreviation EDTA
ethylenediaminetetraacetic acid 相似文献
8.
David M. Glassman 《Primates; journal of primatology》1985,26(3):315-324
Intracortical bone remodeling and cortical thickness data were collected from middiaphyseal thin sections of the humerus,
ulna and tibia for 47 specimens ofSaguinus fuscicollis. Individuals were classified into age cohorts: Young Adult, Mid-adult I, Mid-adult II and Old Adult. Correlation analyses
revealed significant relationships between age cohort and the number of osteons for the humerus and ulna, and between age
cohort and non-Haversian canals for each of the three long bone elements. Significant relationships between age cohort and
dimension of cortex size suggested an age-related pattern of cortical shifting in the ulna and older-age bone loss in the
tibia. 相似文献
9.
Lars Olof Björn 《Physiologia plantarum》1984,60(3):369-372
Experiments by several authors on the effects of polarized light on phytochromemediated responses in fern gametophytes and in the green alga Mougeotia have earlier been interpreted as showing that the transition moment of phytochrome in the Pr form is parallel to the plasmalemma, but perpendicular to the plasmalemma for the Pfr form of phytochrome. It is now shown that the experimental results can be interpreted differently, and that they are also consistent with a chromophore rotation of about 30° (instead of 90°), as found for immobilized phytochrome molecules in vitro. Thus there is no evidence for a rotation of the whole phytochrome protein. For the gametophyte of Adiantum it is calculated that the Pr transition moment is inclined 17° to the plasmalemma, and the Pfr transition moment ca 50°, corresponding to an in vivo chromophore rotation of ca 33°; however, these values are very approximate. 相似文献
10.
Conidiation in Alternaria cichorii Nattras is reversibly stimulated by near ultraviolet radiation (NUV, ca 313 nm) and inhibited by blue light (ca 450 nm) and seems to be a mycochrome-mediated process. After induction with plane-polarized NUV, blue light polarized perpendicularly to the NUV was more effective in counteracting the induction than was blue light polarized parallel to the NUV. From this the conclusions are drawn that (a) both the blue-absorbing component (presumably a flavo-protein) and the PNUV of the mycochrome system are membrane-bound and that (b) the transition moment associated with blue light absorption in the presumed flavoprotein forms an angle of at least 53° with the transition moment associated with NUV absorption in PNUV . 相似文献