全文获取类型
收费全文 | 532745篇 |
免费 | 59657篇 |
国内免费 | 345篇 |
专业分类
592747篇 |
出版年
2018年 | 5219篇 |
2017年 | 5085篇 |
2016年 | 6940篇 |
2015年 | 8765篇 |
2014年 | 10479篇 |
2013年 | 15245篇 |
2012年 | 16950篇 |
2011年 | 17329篇 |
2010年 | 11692篇 |
2009年 | 10733篇 |
2008年 | 15142篇 |
2007年 | 15702篇 |
2006年 | 14668篇 |
2005年 | 14055篇 |
2004年 | 13917篇 |
2003年 | 13280篇 |
2002年 | 12806篇 |
2001年 | 28357篇 |
2000年 | 28212篇 |
1999年 | 21976篇 |
1998年 | 6722篇 |
1997年 | 7303篇 |
1996年 | 6733篇 |
1995年 | 6214篇 |
1994年 | 5984篇 |
1993年 | 5967篇 |
1992年 | 17050篇 |
1991年 | 16299篇 |
1990年 | 15705篇 |
1989年 | 15213篇 |
1988年 | 13924篇 |
1987年 | 12941篇 |
1986年 | 12045篇 |
1985年 | 11825篇 |
1984年 | 9660篇 |
1983年 | 8085篇 |
1982年 | 6000篇 |
1981年 | 5377篇 |
1980年 | 5098篇 |
1979年 | 8946篇 |
1978年 | 6812篇 |
1977年 | 6273篇 |
1976年 | 5648篇 |
1975年 | 6241篇 |
1974年 | 6759篇 |
1973年 | 6543篇 |
1972年 | 5981篇 |
1971年 | 5432篇 |
1970年 | 4682篇 |
1969年 | 4403篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
241.
The photoacoustic spectroscopic studies of purple pigmented leaves revealed the occurrence of anthocyanins and betalains in
some local weed species growing on soils with low moisture levels. The pigmentation intensities were higher in C4 plants than in C3 plants. An inverse correlation was observed between pigmentation intensities and soil moisture levels.
This work is a part of the UNEP Research Project granted to Prof. D. O. Hall, UNEP Coordinator, Department of Plant Sciences,
King’s College; London. 相似文献
242.
N D Klimchuk M S Kitsara O M Frolova N M Balaeva 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1985,(2):41-45
Experiments on the laboratory cultures of lice infected by Weigl's method revealed that the spontaneous, erythromycin-resistant mutant of R. prowazekii strain E, adapted to the vector's organism, retained its resistance to erythromycin during 50 successive passages without the maintenance concentrations of this antibiotic. The above strain remained sensitive to tetracycline and levomycetin. Its level of sensitivity to the latter antibiotics was similar to that of R. prowazekii strains cultivated in the vector's organism for a long time. 相似文献
243.
S Kumar M Antony N K Mehrotra 《Biochemical and biophysical research communications》1984,125(3):967-973
Single cutaneous application of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) increased epidermal oxidised glutathione reductase activity in adult mouse by almost 100%. Pretreatment of animals with vitamin A for a week resulted in 75% inhibition of TPA induced change in the enzyme activity which remained unaffected in skin treated with vitamin A alone. This biochemical change in skin induced by TPA and modulated by vitamin A has been discussed in relation to epidermal hyperplasia. 相似文献
244.
Selective staining of human platelet glycoproteins using nitrocellulose transfer of electrophoresed proteins and peroxidase-conjugated lectins 总被引:3,自引:0,他引:3
Platelet proteins (0.5-5 micrograms) were electrophoresed in a one-dimensional or an unreduced-reduced, two-dimensional sodium dodecyl sulfate gel system. The separated proteins were then transferred electrophoretically to nitrocellulose and reacted with peroxidase-conjugated lectins. Visualization of specific glycoproteins which bound the lectins was made by the chromogenic reaction catalyzed by peroxidase utilizing 3,3'-diaminobenzidine as the substrate. Wheat germ agglutinin specifically reacted with and allowed the visualization of glycoprotein Ib. Peanut agglutinin also specifically stained glycoprotein Ib after treatment of the nitrocellulose transferred proteins with neuraminidase. Ricinus communis agglutinin I stained thrombospondin, a 260 kDa protein, and factor VIII. Concanavalin A stained mainly glycoproteins IIb, III, IV, and V. Glycoproteins Ia, Ic, IIa, and other minor glycoproteins could be separated by unreduced-reduced, two-dimensional gel electrophoresis and were stained weakly with wheat germ agglutinin conjugates. These techniques were found to be reproducible as well as easily applied to the analysis and identification of platelet glycoproteins, particularly when dealing with a limited amount of platelets. 相似文献
245.
J S Garrow 《BMJ (Clinical research ed.)》1983,286(6379):1684-1686
246.
247.
I V Kudriashova D B Logunov O S Papsuevich R I Kruglikov 《Biulleten' eksperimental'no? biologii i meditsiny》1985,99(1):5-7
Perfusion of the snail (Helix lucorum L.) CNS with DG-AVP (concentration 10(-6) M) in the course of low frequency intracellular stimulation (2-4-minute interval) of the defensive reflex command neurons led to an increase in the excitability. It was expressed both in the reduction of the spike generation latency, in the increased number of spikes in response to fixed stimuli, and in the activation of pacemaker potentials. If DG-AVP was added to the medium during endoneuronal habituation, there was no increase in the excitability. It is supposed that modification of the neuronal excitability may be caused by the DG-AVP effect on the pacemaker mechanism. 相似文献
248.
The influence of wilting on the levels of free proline, soluble proteins, reducing sugars, starch and on the activities of
nitrate reductase, invertase, amylase and pyrophosphatases have been studied in the leaf tissue of five cultivars of pearl
millet at their vegetative stage under pot culture conditions. The metabolic changes could not be correlated with the yield
behaviour of the cultivars under a drought condition in the field. 相似文献
249.
S I Zakharov K Iu Bogdanov L V Rozenshtraukh 《Biulleten' eksperimental'no? biologii i meditsiny》1984,97(6):643-645
The existence of mechanical noise (MN) has been demonstrated in isolated papillary muscles of rats at rest. The mean amplitude of the MN was about 1 mg, the mean frequency 1.5 Hz (t 22 degrees C). A good agreement was found between the MN amplitude and the contracture level of the muscle. However, during long contractures, the correlation between the noise and contracture magnitude was disturbed. There was no relationship between the MN amplitude and contracture magnitude during exposures inducing metabolic alterations (hypoxia, NaCN) and upsetting the work of the sarcoplasmic reticulum (caffeine). It is believed that the MN amplitude is in a good agreement with the contracture magnitude and, therefore, with the concentration of intracellular Ca2+, if the sarcoplasmic reticulum and contractile elements of the cells are intact. 相似文献
250.
Morphological taxonomy of simple Hyphomycetes is complicated by the frequent occurrence of pleoanamorphism. In some groups
of yeast-like fungi, uncommon synanamorphs are diagnostic. Differences in conidiogenesis do not always delimit natural groups.
Some nomenclatural problems are mentioned, with an emphasis on the need of neotypification. Prospects are sketched for future
taxonomic research. 相似文献