全文获取类型
收费全文 | 14699篇 |
免费 | 1240篇 |
国内免费 | 25篇 |
出版年
2022年 | 104篇 |
2021年 | 213篇 |
2020年 | 140篇 |
2019年 | 169篇 |
2018年 | 258篇 |
2017年 | 223篇 |
2016年 | 305篇 |
2015年 | 425篇 |
2014年 | 547篇 |
2013年 | 856篇 |
2012年 | 809篇 |
2011年 | 777篇 |
2010年 | 466篇 |
2009年 | 448篇 |
2008年 | 646篇 |
2007年 | 690篇 |
2006年 | 628篇 |
2005年 | 655篇 |
2004年 | 605篇 |
2003年 | 573篇 |
2002年 | 575篇 |
2001年 | 442篇 |
2000年 | 480篇 |
1999年 | 439篇 |
1998年 | 173篇 |
1997年 | 147篇 |
1996年 | 136篇 |
1995年 | 158篇 |
1994年 | 140篇 |
1993年 | 145篇 |
1992年 | 344篇 |
1991年 | 245篇 |
1990年 | 261篇 |
1989年 | 257篇 |
1988年 | 363篇 |
1987年 | 221篇 |
1986年 | 184篇 |
1985年 | 173篇 |
1984年 | 133篇 |
1983年 | 128篇 |
1982年 | 89篇 |
1981年 | 96篇 |
1979年 | 107篇 |
1978年 | 91篇 |
1977年 | 63篇 |
1976年 | 65篇 |
1975年 | 64篇 |
1974年 | 89篇 |
1973年 | 67篇 |
1972年 | 63篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
The non-Newtonian behavior and dynamic viscoelasticity of a series of aqueous solutions of agarose were measured with a rheogoniometer. The flow curve, at 25°, of agarose solution approximated to plastic behavior at 0.1, 0.13, and 0.15% concentrations. Gelation occurred at concentration of 0.13% at low temperature (0°). The dynamic modulus of agarose showed a very high value at low temperature, and increased with an increase in temperature, showing a maximum value at 30°, then it decreased. In the presence of NaCl, KCl, CaCl2, and MgCl2 for a solution of agarose at 0.08% concentration, the transition temperature, at which dynamic modulus decreased rapidly, was observed at 60°. Gelation was also observed at low temperature (0°) in acid and alkaline range after reaching pH values of 2.3 and 9.5, respectively, by addition of 100m
HCl, H2SO4, NaOH, and Ca(OH)2 to a 0.08% agarose solution. A possible mode of intra- and inter-molecular hydrogen bonding within and between the agarose molecules in aqueous solution is proposed. 相似文献
13.
S. H. Habib S.-E. Ooi Ond?ej Novák Danu?e Tarkowská Jakub Rol?ík Karel Dole?al S. S. R. Syed-Alwee C.-L. Ho P. Namasivayam 《Plant Growth Regulation》2012,68(2):313-317
Comparative mineral and hormonal analyses were made on tissue culture derived truncated leaf syndrome and wild type oil palm seedlings. Mineral analysis confirmed that Boron, Zinc and chlorophyll levels were significantly lower in truncated leaf syndrome leaves than those of wild type. Hormonal analysis also revealed various cytokinin derivatives such as trans-zeatin, trans-zeatin riboside, trans-zeatin O-glucoside and trans-zeatin riboside 5??mono phosphate were significantly higher in truncated leaf syndrome leaves compared to wild type leaves. Brassinolide level was also significantly higher in truncated leaf syndrome leaves than those of the wild type. These observations suggest that the truncated leaf syndrome abnormality could be associated to high cytokinin and brassinosteroid production which affects the uptake of Boron and Zinc. 相似文献
14.
W Nakamura Y Nagano K Otsuka Y Nishimoto 《Comptes rendus des séances de la Société de biologie et de ses filiales》1980,174(1):104-107
The interferon inducing effect of hyperthermia was studied in normal and tumor-bearing mice. Circulating interferon was temporarily detected one day after subcutaneous transplantation of 1.6 X 10(6) Ehrlich's ascites tumor cells. Hyperthermia of 43.5 degrees C for 5 min did not induce the interferon formation in mice with or without subcutaneous tumor of the cells. These findings showed that the induction of interferon formation was not main cause of the hyperthermia-induced tumor inhibition. 相似文献
15.
The purpose of our investigation was to clarify the effects of agriculture on the process of loss of litter at the periphery of a farmland. This study revealed the generation process of an ecologically unusual phenomenon that is observed around cropland in semi-arid regions. We hypothesized that the vegetation around a farmland cannot supply plant litter to the ground surface because the ecological structure has been changed by agricultural activities. The study was conducted at Xilingol steppe, Xilingol League, Inner Mongolia Autonomous Region, China. Four study lines were established from the edge of an arable field to the surrounding meadow and parallel to the wind direction during the strong wind season. Key measurement for each line was set at the border between the farmland and steppe. Four study sites were set at intervals along each line. Plant litter, soil particle size distribution, plant species composition, plant volume, and species diversity were investigated. Despite using the same mowing method at the meadows of all study sites, the litter at the only periphery of the farmland completely disappeared. Soil particle size distribution in steppe, which was adjacent to the farmland, was similar to that of the farmland. Plant community structure at the periphery of the farmland was different from that of the far side from the farmland. This implies that soil scattered from the farmland affected the species composition of the steppe. Consequently, the change in plant community structure induced litter loss because of mowing. We concluded that plant litter was lost near the farmland because of the combined effects of farming and mowing. The results support our hypothesis that the vegetation around a farmland cannot supply plant litter because the ecological structure has been changed by agricultural activities. 相似文献
16.
Several modification of the arrangements of α-helical molecules were found in the solid films of poly (γ-ethyl-L -glutamate), depending on the casting solvent and the temperature. The helical conformation is somewhat looser than the normal 18-residue, 5-turn α-helix. Using x-ray diffraction, the types of molecular arrangements were classified into tetragonal, pseudohexagonal, and hexagonal ones. Tetragonal packing was observed in the filmm (form T) prepared by casting the solution in trifluorethanol or dichlorethane. The sample obtained from chloroform solution is a well-ordered, pseudohexagonal modification (form I). Forms I and T change into a poorly crystalline form III by annealing at temperatures above 130° C. It is particularly noteworthy that the less-ordered form III exhibits a thermoreversible transition around 110°C into a well-ordered form H with the hexagonal molecular packing. 相似文献
17.
18.
Aimée Watt Smyth 《BMJ (Clinical research ed.)》1907,2(2439):849-850
19.
20.