全文获取类型
收费全文 | 169490篇 |
免费 | 4839篇 |
国内免费 | 820篇 |
出版年
2023年 | 458篇 |
2021年 | 939篇 |
2020年 | 848篇 |
2019年 | 820篇 |
2018年 | 13364篇 |
2017年 | 12002篇 |
2016年 | 9721篇 |
2015年 | 4013篇 |
2014年 | 3793篇 |
2013年 | 4937篇 |
2012年 | 9432篇 |
2011年 | 17025篇 |
2010年 | 14546篇 |
2009年 | 10133篇 |
2008年 | 13136篇 |
2007年 | 14498篇 |
2006年 | 3799篇 |
2005年 | 3490篇 |
2004年 | 3943篇 |
2003年 | 3677篇 |
2002年 | 3218篇 |
2001年 | 2266篇 |
2000年 | 2049篇 |
1999年 | 1474篇 |
1998年 | 639篇 |
1997年 | 469篇 |
1996年 | 516篇 |
1992年 | 931篇 |
1991年 | 865篇 |
1990年 | 823篇 |
1989年 | 896篇 |
1988年 | 745篇 |
1987年 | 763篇 |
1986年 | 685篇 |
1985年 | 749篇 |
1984年 | 628篇 |
1983年 | 560篇 |
1979年 | 671篇 |
1978年 | 488篇 |
1977年 | 488篇 |
1975年 | 589篇 |
1974年 | 625篇 |
1973年 | 596篇 |
1972年 | 795篇 |
1971年 | 768篇 |
1970年 | 542篇 |
1969年 | 612篇 |
1968年 | 573篇 |
1967年 | 480篇 |
1966年 | 467篇 |
排序方式: 共有10000条查询结果,搜索用时 312 毫秒
851.
J M Fernández M F Rubio-Arroyo M Soriano-García R A Toscano M C Pérez-César 《Steroids》1985,45(2):151-157
The synthesis and molecular structure of prolame, N-(3-hydroxy-1,3,5(10)-estratrien-17 beta-yl)-3-hydroxypropylamine, is described. It was characterized by ir, nmr, mass spectrometry and chemical analysis. The crystal structure of this compound was determined by single-crystal x-ray diffraction. Prolame belongs to space group P212121. Cell dimensions are: a = 8.356(2), b = 13.343(4) and c = 16.119(4) A. Z = 4; R = 4.1%. 相似文献
852.
Trifluoperazine was administered to pregnant mice and rats by gastric intubation during the period of organogenesis. Dams were treated at doses of 0.5, 5, 50 (mice and rats) and 100 (only rats) mg/kg/day. The drug affected the pregnant weight increment in a dose-related manner in rats but only the 50 mg/kg/day dose level affected the weight gain of mice. The foetal weight was not markedly affected in either species. The drug induced cleft palate and micrognathia in rats but did not produce a teratogenic effect in mice. Trifluoperazine caused abortions in mice and there were significant increases in the number of resorptions with the top dose levels in both species. 相似文献
853.
N Akimenko P Cheltsov Z Balcarová V Kleinw?chter Y u Yevdokimov 《General physiology and biophysics》1985,4(6):597-608
The optical properties of the DNA complexes with divalent platinum compounds of the cis-diamine type differing both in the nature of anionic and neutral ligands and in the spatial arrangement about the platinum atom were studied. The platinum compounds cis-[Pt(NH3)2Cl2], [Pt(en)Cl2], [Pt(tetrameen)Cl2], cis-[Pt(NH3)2NO2Cl], and cis-[PtNH3(Bz)Cl2] at small values of r (r is the molar ratio of a platinum compound to DNA nucleotides in the reaction mixture) were found to induce an increase in the amplitude of the positive band in the circular dichroic (CD) spectrum of linear DNA. All the compounds listed except cis-[Pt(NH3)2NO2Cl] caused a sharp decrease of the amplitude of the negative band in the CD spectrum of a liquid crystalline microphase of DNA formed in solution in the presence of poly(ethylene glycol). All these platinum compounds (except [Pt(tetrameen)Cl2]) exhibit biological (antimitotic, antitumour, etc.) activity. The platinum compounds trans-[Pt(NH3)Cl2], trans-[Pt(NH3)2NO2Cl], cis-[PtNH3PyCl2], cis-[Pt(NH3)2(NO2)2], and [Pt(NH3)3Cl]Cl exhibiting a low (if any) biological activity, either induced a decrease of the amplitude of the positive band in the CD spectrum of linear DNA, or did not affect the CD spectrum at all. The effect of these platinum compounds on the CD spectrum of the liquid crystalline microphase of DNA was either weak or absent. It is assumed that the specific biological action of platinum compounds of the cis-diamine type is determined by the polydentate binding to DNA: in addition to the cis-bidentate covalent binding of platinum to DNA nitrogen bases, a hydrogen bond formation between the DNA and cis-amino ligands occurs by means of protons at nitrogen atoms. 相似文献
854.
855.
L Vyklicky L Vyklicky F Vyskocil E Ujec J Michl V Vlachová 《General physiology and biophysics》1985,4(3):241-248
Single-channel K+ currents were studied in the myotubes from the chick embryo grown in tissue culture for 4--9 days by employing the patch clamp technique. The "cell attached" configuration was used and the pipette was filled with a solution containing 3 mmol.l-1 K+. The channels exhibited a high conductance of approximately 90 pS and the probability of finding them open increased by an e-fold factor for 13 mV depolarization for low levels of activity. The channels did not inactivate during long-lasting depolarization. These channels have been suggested to contribute to delayed rectification. 相似文献
856.
Principal component analysis for a better understanding of the herbicidal effectivity of some benzonitriles 总被引:1,自引:0,他引:1
To gain more insight in mode of action of ten different 4-hydroxy-benzonitrile derivatives, their biological activities in eight bioassays, and their lipophilicity and adsorptivity determined by thin-layer chromatography in nine different systems were subjected to principal component analysis. Four background components explained about 90% of total variance. Only three of eight biological activities, the inhibition of the 2,6-dichlorophenol-indophenol reduction by spinach and wheat chloroplasts and the CO2 fixation of wheat seedlings had not any common background components with the physico-chemical parameters of the compounds. The nonlinear mapping of principal component loadings and variables showed, that the in vivo and in vitro biological activities differed considerably and depended on the object investigated. The effectivity of compounds is governed mainly by the number of substituents and by the presence of free hydroxy group. 相似文献
857.
Mitochondrial glycerol 3-phosphate dehydrogenase (EC 1.1.2.1.) requires Ca2+ ions for its activity. Cadmium ions also have activatory effect on the enzyme. They activate the glycerol 3-phosphate dehydrogenase in a very narrow concentration range (1-2 mmol/l). As contrasted with calcium, strong inhibitory effect occurred at higher concentrations (3-4 mmol/l). The inhibition induced by cadmium ions was completely reversible by washing of the mitochondria. 相似文献
858.
The effect of unilateral renal sympathectomy on renal excretion of water and sodium was studied in three groups of Inactin-anaesthetized rats: 1-3, 4-19, and 20-35 weeks after denervation. Increased sodium excretion from the denervated kidney in the absence of changes in GFR was observed up to 35 weeks following renal denervation. Thus, in a functional sense, renal reinnervation may have only been partial during the time interval studied. 相似文献
859.
C Farsang J Kapocsi K Varga L Vajda A Balás-Eltes G Kunos 《Acta physiologica Hungarica》1985,65(2):217-226
Analysis of the effect of naloxone (0.4 mg iv.) on clonidine hypotension in 80 patients with essential hypertension revealed that two groups could be separated. In the responding group (43 pts) naloxone increased blood pressure and heart rate in clonidine-treated patients while in the non-responding group (37 pts) it has no such effect. Patients in the responding group had higher cardiac output, stroke volume, plasma renin activity, plasma adrenaline and beta-endorphin levels and lower total peripheral resistance, shorter history of hypertension and lesser body weight than those in the non-responding group. The pressor effect of naloxone in four responding patients treated with clonidine for 29 months tended to be smaller compared to the response obtained after a 3-day clonidine therapy. Results favour the hypothesis of the existence of two (responding, non-responding) groups of patients with essential hypertension. Further work will clarify whether these groups represent different pathogenesis or they indicate only a different stage of hypertension. 相似文献
860.
Margarita F. Renart Leandro Sastre Víctor Díaz Jésus Sebastián 《Molecular and cellular biochemistry》1985,66(1):21-29
Summary A purification procedure to obtain RNA polymerases I (or A) and II (or B) from Dictyostelium discoideum amoeba has been developed. The enzymes were solubilized from purified nuclei and separated by DEAF-Sephadex chromatography. RNA polymerases I and II were further purified by a second chromatography on DEAE-Sephadex followed by chromatographies on phosphocellulose and heparin-sepharose. The specific activities of purified RNA polymerases I and II are 92 units/ mg protein and 70 units/ mg protein, respectively. The subunit structure of both RNA polymerases were analyzed by polyacrylamide gel electrophoresis under denaturing conditions after glycerol gradient centrifugation of the enzymes. The putative subunits of RNA polymerase I have molecular weights of 180 000,125 000,43 000,40 000,34 000, 31 000, 25 000,19 000, 17 000 and 14 000. The putative subunits of RNA polymerase II have molecular weights of 200 000 (170 000), 130 000, 33 000, 25 000, 19 000, 17 000, 15 000, 13 000. There are three polypeptides with common molecular weight in Dictyostelium RNA polymerases I and 11. The subunit of 25 000 daltons of both enzymes has common immunological determinants with RNA polymerase II from crustacean Artemia.Abbreviations TLCK
tosyl-lysine-chloromethyl-ketone
- DPT
diazophenylthioether 相似文献