全文获取类型
收费全文 | 993595篇 |
免费 | 105715篇 |
国内免费 | 393篇 |
专业分类
1099703篇 |
出版年
2018年 | 9331篇 |
2017年 | 8884篇 |
2016年 | 12492篇 |
2015年 | 16084篇 |
2014年 | 19225篇 |
2013年 | 27503篇 |
2012年 | 30877篇 |
2011年 | 31754篇 |
2010年 | 21588篇 |
2009年 | 20194篇 |
2008年 | 28469篇 |
2007年 | 29587篇 |
2006年 | 27827篇 |
2005年 | 26741篇 |
2004年 | 26498篇 |
2003年 | 25553篇 |
2002年 | 25036篇 |
2001年 | 45256篇 |
2000年 | 45169篇 |
1999年 | 35886篇 |
1998年 | 12754篇 |
1997年 | 13040篇 |
1996年 | 12326篇 |
1995年 | 11372篇 |
1994年 | 10998篇 |
1993年 | 11131篇 |
1992年 | 29228篇 |
1991年 | 28756篇 |
1990年 | 27972篇 |
1989年 | 27357篇 |
1988年 | 25208篇 |
1987年 | 23948篇 |
1986年 | 22283篇 |
1985年 | 22110篇 |
1984年 | 18004篇 |
1983年 | 15782篇 |
1982年 | 11839篇 |
1981年 | 10669篇 |
1980年 | 9968篇 |
1979年 | 16799篇 |
1978年 | 13239篇 |
1977年 | 11983篇 |
1976年 | 11260篇 |
1975年 | 12608篇 |
1974年 | 13432篇 |
1973年 | 13257篇 |
1972年 | 12020篇 |
1971年 | 10868篇 |
1970年 | 9576篇 |
1969年 | 9326篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
981.
982.
Tsyganov V. E.; Pavlova Z. B.; Kravchenko L. V.; Rozov S. M.; Borisov A. Y.; Lutova L. A.; Tikhonovich I. A. 《Annals of botany》2000,86(5):975-981
Using ethyl methane sulfonate (EMS) treatment of the seeds ofline SGE, a new mutant of pea (Pisum sativum L.) with alterationsin root development was obtained. The mutant phenotype dependson the density of the growth substrate: on sand (a high densitysubstrate) the mutant forms a small compact curly root systemwhereas on vermiculite (a low density substrate) differencesbetween the root systems of the mutant and wild type plantsare less pronounced. Genetic analysis revealed that the mutantcarries a mutation in a new pea gene designedcrt (curly roots).Gene crt has been localized in pea linkage group V. The mutantline named SGEcrt showed increased sensitivity to exogenousauxin and an increased concentration of endogenous indole-3-aceticacid (IAA) in comparison with the wild type line SGE. Copyright2000 Annals of Botany Company Pisum sativum L., root development, garden pea mutant, curly roots, auxin, environmental stimulus response 相似文献
983.
Branchingprocess(BP)isusedtomodeltheearlystagesofthespreadofasexuallytransmitteddisease.TheearlystagesofAIDSspreadwhichistransmittedbothhomosexuallyandheterosexuallyarestudiedasaBP. 相似文献
984.
985.
J. L. Wilkens T. Kuramoto 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(7):483-490
The decapod cardiovascular system consists of a single ventricle that pumps blood into seven arteries; previous work has
shown that the outflow distribution patterns of intact animals are variable. In the present study, flow recordings were made
from pairs of arteries in semi-isolated hearts whilst different cardioactive hormones were infused into the heart. Each hormone
(5-hydroxytryptamine, octopamine, dopamine, proctolin and F1) changed the outflow pattern, heart rate and ventricular pressure
in a unique way. The probable sites of hormone action are the cardioarterial valves located at the origin of each artery except
one, the dorsal abdominal. Outflow from the dorsal abdominal is controlled downstream by valves located at the origin of the
segmental lateral arteries. The responses to a particular hormone were sometimes different between the hearts of American
and Japanese lobsters.
Accepted: 11 May 1998 相似文献
986.
987.
Sharbati R. Singh Sunita Dalal Rohtas Singh A. K. Dhawan Rajwant K. Kalia 《Journal of plant biochemistry and biotechnology.》2012,21(2):220-228
Effect of season, media type, carbon source, growth regulators and transplanting media on micropropagation of Dendrocalamus asper, an important bamboo species, was examined. The season of explant collection played an important role in axillary bud sprouting and spring (February?CApril) was found to be the best period for explant collection. Among the different media MS was found to be the best for micropropagation. Maximum numbers (4.83/explant) of shoots were initiated in MS?+?15???M BAP. For shoot multiplication, MS medium supplemented with 10???M BAP and 75???M Adenine sulfate was used. BAP was superior to KIN for both explant establishment, as well as, shoot multiplication. Optimal rooting was achieved in shoots cultured on ? strength MS medium supplemented with 5???M each of IBA and NAA. Regenerated plantlets were acclimatized and hardened in green house using dune sand and vermi-compost (3:1) with 92.34% success and transferred to the field with 100% survival rate. In the field, plants supplied with FYM along with urea showed better growth and development. Macroproliferation, plant multiplication by separating the rooted tillers of well established in vitro raised plantlets after 5 to 6?months of growth in the green house could double the multiplication rate. More than 25000 in vitro raised plants were successfully transferred to the field and no morphological variations in growth were observed, thus proving the potential of tissue culture for raising large scale plantations of D. asper. 相似文献
988.
The p53 pathway and apoptosis. 总被引:17,自引:0,他引:17
989.
J. M. Fryxell T. Crease A. W. Illius 《Proceedings. Biological sciences / The Royal Society》1999,266(1425):1277
The maintenance of genetic variability in morphological traits that affect fitness is poorly understood. We present a simple Mendelian model of genetic traits affecting foraging efficiency in grazing ungulates, based on a trade-off between rates of energy extraction at low versus high levels of plant abundance. The model suggests that variation in foraging efficiency could be maintained via lottery competition arising as a direct consequence of dynamically unstable interactions between consumers and their food resources. Lottery competition is a plausible mechanism for explaining wide variability in foraging efficiency, such as that documented in unstable Soay sheep populations on the St Kilda archipelago. 相似文献
990.
Temperature affects both the biology and morphology of mosquito vectors. Geometric morphometrics is a useful new tool for capturing and analyzing differences in shape and size in many morphological parameters, including wings. We have used this technique for capturing the differences in the wings of the malaria vector Anopheles superpictus, using cohorts reared at six different constant temperatures (15°, 20°, 25°, 27°, 30°, and 35° C) and also searched for potential correlations with the life tables of the species. We studied wing shape in both male and female adults, using 22 landmarks on the wing in relation to ecological parameters, including the development rate. The ecological zero was calculated as 9.93° C and the thermal constant as 296.34 day‐degrees. The rearing temperature affects egg, larval, and pupal development and also the total time from egg to adult. As rearing temperatures increased, longevity decreased in both sexes. In An. superpictus, Ro value and productivity correlated with the statistically significant gradual deformations in the wing shape related to size in both sexes. These deformations directly linked to differences in immature rearing temperatures. Analysis using PCA and UPGMA phenograms showed that although wings of females became narrower dorsoventrally as the temperature increased, they became broader in males. Comparisons of the wing landmarks indicated the medial part of the wing was most affected by larval rearing temperatures, showing relatively more deformations. Algorithmic values of the life tables were determined in correlation with the results of geometric morphometrics. Comparisons of centroid sizes in the cohorts showed that overall wing size became smaller in both sexes in response to higher rearing temperatures. 相似文献