全文获取类型
收费全文 | 296144篇 |
免费 | 22497篇 |
国内免费 | 327篇 |
专业分类
318968篇 |
出版年
2018年 | 8283篇 |
2017年 | 8127篇 |
2016年 | 7146篇 |
2015年 | 3877篇 |
2014年 | 4605篇 |
2013年 | 6579篇 |
2012年 | 9290篇 |
2011年 | 14424篇 |
2010年 | 10669篇 |
2009年 | 9968篇 |
2008年 | 12226篇 |
2007年 | 13925篇 |
2006年 | 6788篇 |
2005年 | 7280篇 |
2004年 | 6960篇 |
2003年 | 7040篇 |
2002年 | 6837篇 |
2001年 | 12123篇 |
2000年 | 12138篇 |
1999年 | 9144篇 |
1998年 | 2673篇 |
1997年 | 2758篇 |
1996年 | 2712篇 |
1995年 | 2476篇 |
1994年 | 2427篇 |
1993年 | 2343篇 |
1992年 | 7189篇 |
1991年 | 7005篇 |
1990年 | 7060篇 |
1989年 | 6856篇 |
1988年 | 6357篇 |
1987年 | 6018篇 |
1986年 | 5355篇 |
1985年 | 5661篇 |
1984年 | 4471篇 |
1983年 | 3876篇 |
1982年 | 2682篇 |
1981年 | 2493篇 |
1980年 | 2303篇 |
1979年 | 4107篇 |
1978年 | 3134篇 |
1977年 | 2881篇 |
1976年 | 2826篇 |
1975年 | 3278篇 |
1974年 | 3496篇 |
1973年 | 3524篇 |
1972年 | 3630篇 |
1971年 | 3347篇 |
1970年 | 2536篇 |
1969年 | 2299篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
142.
The use of modernized photometric accessories to a model microscope manufactured by the Leningrad Optico-Mechanical Amalgamation (USSR), as well as the practical application of innovations facilitating and standardizing research work, has made it possible to obtain objective data indicating the presence of significant, direct, linear correlation between infectious activity and the intensity of fluorescence emitted by fluorescent antibodies bound with the antigen of 11 studied variants of Japanese encephalitis virus in continuous cell lines. The study of the dynamics of fluorescence intensity permitted the objective evaluation of the previously revealed regularity in the increase of the intensity of the induced fluorescence of Japanese encephalitis antigen in continuous cell cultures. 相似文献
143.
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
144.
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
145.
146.
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
147.
148.
Phase-sensitive two-dimensional nuclear Overhauser effect spectra of [d(GGTATACC)]2 in aqueous deuterium oxide solution at four mixing times were quantified to give all nonoverlapping cross-peak intensities. A structural model for [d(GGTATACC)]2 was built in which the GG- and -CC moieties were in the B-DNA form, while the middle -TATA- moiety was in the wrinkled-D form (BDB model). This model was subjected to energy refinement by molecular mechanics calculations with the program AMBER. Counterions (Na+) were added to neutralize the charges, and water molecules were placed bridging across the minor groove. A complete relaxation matrix analysis was used to calculate two-dimensional nuclear Overhauser effect spectra of [d(GGTATACC)]2 from the above models (before and after energy refinement) and from four other [d(GGTATACC)]2 structural models: regular A, crystalline A, regular B, and energy-minimized B. Among them, the energy-minimized BDB model yielded a set of theoretical spectra that gave the best fit to the experimental spectra. It was also the energetically most stable. Therefore, it is a good representation of the ensemble- and time-averaged structure of the octamer in solution. This model has backbone torsion angles similar to those of B-form DNA in the GG- and -CC moieties and torsion angles similar to those of wrinkled D form DNA in the -TATA- moiety. The base stacking and base pairing are not interrupted at the junctions between the two structural moieties. Its minor groove is narrower than that of B DNA, and the solvent-accessible surface of the minor groove forms a closed hydration tunnel in the middle -TATA- segment. 相似文献
149.
N A Markovich T I Vorotyntseva M I Zil'berman V K Antonov 《Biokhimii?a (Moscow, Russia)》1985,50(5):795-803
Cathepsin D was purified from the lactating rabbit mammary gland by a rapid procedure, which included fractionation with (NH4)2SO4, acid precipitation, double affinity chromatography on pepstatin-Sepharose 4B and gel filtration on Sephadex G-100, resulting in approximately 360-fold purification of the enzyme over the homogenate and approximately 16% recovery. After isoelectric focusing, the enzyme dissociated into four (pI 5.8, 6.3, 6.5 and 7.2) multiple forms, but appeared homogeneous on polyacrylamide gel electrophoresis. Cathepsin D has a Mr of 45 kDa as determined by Sephadex G-100 column chromatography. On sodium dodecylsulfate/polyacrylamide gel electrophoresis the enzyme gave a single protein band, corresponding to Mr of 45 kDa. The amino acid composition of the enzyme is similar to that of cathepsins D from other tissues. A single N-terminal amino acid was glycine. Cathepsin D contains 6.4% carbohydrates consisting of mannose, galactose, fucose and glucosamine at a ratio of 3:9:2:2. Cathepsin D is inhibited by pepstatin with Ki of 2.5 X 10(-9) M and irreversibly by N-diazoacetyl-N'-2.4-dinitrophenyl-ethylene diamine. The enzyme hydrolyzes bovine hemoglobin with the maximal activity at pH 3.0 with Km = 10(-5) M and HLeu-Ser-Phe(NO2)-Nle-Ala-Leu-OMe with Km = 4 X 10(-5) M and Rcat = 0.95 s-1. The major cleavage sites were Leu15-Tyr16, Phe24-Phe25 and Phe25-Tyr26 during hydrolysis of the oxidized insulin B-chain by cathepsin D. 相似文献
150.
V E Kagan E A Serbinova A A Minin V M Savov K N Novikov 《Biokhimii?a (Moscow, Russia)》1985,50(6):986-991
The localization and mechanism of generation of active oxygen species in the enzymatic NADPH-dependent lipid peroxidation system in liver microsomes were studied. Using the spin-trapping method, the key role of active oxygen species in the initiation of NADPH-dependent enzymatic lipid peroxidation was confirmed. It was shown that active oxygen species are generated via consecutive one-electron reduction of the oxygen molecule by NADPH-cytochrome P-450 reductase. 相似文献