全文获取类型
收费全文 | 701263篇 |
免费 | 75521篇 |
国内免费 | 1272篇 |
出版年
2018年 | 6611篇 |
2016年 | 8506篇 |
2015年 | 11475篇 |
2014年 | 13510篇 |
2013年 | 19587篇 |
2012年 | 21357篇 |
2011年 | 21847篇 |
2010年 | 14629篇 |
2009年 | 13275篇 |
2008年 | 18812篇 |
2007年 | 19698篇 |
2006年 | 18422篇 |
2005年 | 17616篇 |
2004年 | 17623篇 |
2003年 | 17100篇 |
2002年 | 16762篇 |
2001年 | 28564篇 |
2000年 | 28602篇 |
1999年 | 23086篇 |
1998年 | 8439篇 |
1997年 | 8734篇 |
1996年 | 8317篇 |
1995年 | 7989篇 |
1994年 | 7815篇 |
1993年 | 7682篇 |
1992年 | 20084篇 |
1991年 | 19547篇 |
1990年 | 19471篇 |
1989年 | 18992篇 |
1988年 | 17870篇 |
1987年 | 16919篇 |
1986年 | 15644篇 |
1985年 | 16154篇 |
1984年 | 13317篇 |
1983年 | 11612篇 |
1982年 | 9029篇 |
1981年 | 8049篇 |
1980年 | 7628篇 |
1979年 | 13088篇 |
1978年 | 10064篇 |
1977年 | 9457篇 |
1976年 | 8918篇 |
1975年 | 9692篇 |
1974年 | 10583篇 |
1973年 | 10540篇 |
1972年 | 9708篇 |
1971年 | 8975篇 |
1970年 | 7655篇 |
1969年 | 7593篇 |
1968年 | 6948篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Abstract The parasitoid wasp Trichogramma dendrolimi Matsumura sets the number of progeny allocated to its insect egg hosts according to the duration of its initial transit walk across the host surface. Although cooling the wasp reduces its walking speed, reduced temperature does not affect progeny allocation. By locally heating and cooling the wasps, the initial transit can be thermally uncoupled from the subsequent oviposition. Using this technique we show that the timing of initial transit duration is temperature-dependent. These findings suggest that short interval timing by Trichogramma differs physiologically from the temperature compensated clocks that have been described for other insects. 相似文献
972.
The combination of alpha interferon and vinblastine has been reported to yield a response rate of 30-40% in previously untreated patients with metastatic renal cell carcinoma. This combination was given to nine patients with advanced metastatic renal carcinoma after they failed or relapsed on alpha-interferon alone, to attempt to evaluate the role of vinblastine in this combination. Neither complete nor partial response was observed. Two patients had disease stabilization for two and seven months. Our preliminary results suggest that vinblastine did not add to the efficacy of interferon in this group of patients. 相似文献
973.
974.
B P Sharonov I V Churilova 《Biochemical and biophysical research communications》1992,189(2):1129-1135
Bovine superoxide dismutase (SOD) was inactivated during incubation with phorbol myristate acetate-stimulated neutrophils. In addition, stimulated neutrophils were able to disrupt the SOD structure. Inactivation and structural damage were dependent on the action of hypochlorous acid, an oxidant generated by the myeloperoxidase-hydrogen peroxide-chloride system of neutrophils. Incubation of SOD with stimulated neutrophils lead to long-wavelength fluorescence (ex, 350 nm; em, 450 nm) and the appearance of new structural forms with other isoelectric points. These additional forms possess catalytic activity. Generation of catalytically active new forms of SOD demonstrates the inaccessibility of the active centre of SOD to hypochlorite and may be a reason for the successful application of SOD during anti-inflammatory therapy. 相似文献
975.
Disease resistance, stress response and effects of triploidy in growth hormone transgenic coho salmon 总被引:2,自引:0,他引:2
Diploid and triploid coho salmon Oncorhynchus kisutch transgenic for growth hormone (GH) and control coho salmon were compared for differences in disease resistance and stress response. Resistance to the bacterial pathogen Vibrio anguillarum was not affected in transgenic fish relative to their non‐transgenic counterparts when they were infected at the fry stage, but was lower in transgenic fish when infected near smolting. Vaccination against vibriosis provided equal protection to both transgenic and non‐transgenic fish. Triploid fish showed a lower resistance to vibriosis than their diploid counterparts. Diploid transgenic fish and non‐transgenic fish appeared to show similar physiological and cellular stress responses to a heat shock. These studies provide information useful for both performance and ecological risk assessments of growth‐accelerated coho salmon. 相似文献
976.
G. N. Mishina G. V. Serezhkina T. V. Avetisyan A. S. Ryabchenko L. N. Andreev 《Biology Bulletin》2001,28(4):354-360
A cytophysiological study was carried out of the functional status of a halo as a response of the host plant to contact with a powdery mildew pathogen. Interactions of the powdery mildew causative agents with barley, wheat, wheat–wheat-grass hybrids, wheat-aegilops lines, and aegilops with different genotypic resistance lead to the expression of haloes during pathogens, which are induced by infection pegs of the primary growth tubes, appressoria, and hyphal lobes. Haloes are visualized using cytochemical reactions to proteins and scanning electron microscopy. The observed differences in the size of haloes and intensity of their staining (uniform or zonal) are related, to a great extent, to individual reactions of the plant cell at the penetration site and, to a lesser extent, to the level of genotypic resistance. An analysis of electron microscopy and cytochemistry studies suggests that the halo as a physiologically active zone is localized at the level of the plant cell plasmalemma. Active taxis of the cell organelles to the site of infection during the formation of a halo suggests that some kind of informational signals to changes in the cell metabolism are spread from the halo zone, which lead to compatible or incompatible interactions. 相似文献
977.
Phytochrome A regulates red-light induction of phototropic enhancement in Arabidopsis. 总被引:20,自引:5,他引:15 下载免费PDF全文
Phytochrome A (phyA) and phytochrome B photoreceptors have distinct roles in the regulation of plant growth and development. Studies using specific photomorphogenic mutants and transgenic plants overexpressing phytochrome have supported an evolving picture in which phyA and phytochrome B are responsive to continuous far-red and red light, respectively. Photomorphogenic mutants of Arabidopsis thaliana that had been selected for their inability to respond to continuous irradiance conditions were tested for their ability to carry out red-light-induced enhancement of phototropism, which is an inductive phytochrome response. We conclude that phyA is the primary photoreceptor regulating this response and provide evidence suggesting that a common regulatory domain in the phyA polypeptide functions for both high-irradiance and inductive phytochrome responses. 相似文献
978.
Socioeconomic, demographic and environmental determinants of infant mortality in Nepal 总被引:1,自引:0,他引:1
The Nepal Fertility and Family Planning Survey of 1986 demonstrated that demographic variables, previous birth interval and survival of preceding child, still predominated as determinants of infant mortality, particularly in rural areas of Nepal. However, in urban Nepal, where the level of socioeconomic development is higher, an environmental variable, along with previous birth interval and survival of preceding child emerges as important in determining infant mortality. Separate policy measures for child survival prospects in rural and urban Nepal are suggested. 相似文献
979.
980.
M G Lee 《Molecular and cellular biology》1996,16(3):1220-1230