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201.
For the model y = α + βx + ? (model I) of linear regression we dealt with in KUHNERT and HORN (1980) the determination of a confidence interval for that x0 where the expectation Ey reaches a given value y0. Here we start with realizations of random variables y (i = 1,…, m) being independent of x which are given in addition to the realizations of-y. Now y0 denotes the unknown value of \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \sum \limits_{i = 1}^m $\end{document} ciEy and x0 the x-value where the expectation Ey reaches that value y0. For this x0 we give a confidence interval. Applications stem from dose response assays. 相似文献
202.
Mg2+ restores membrane potential in rat liver mitochondria deenergized by Ca2+ and phosphate movements 总被引:1,自引:0,他引:1
Cellular ornithine biosynthesis could be expected to play a significant role in putrescine formation and hence in growth. Two enzymes are involved in ornithine biosynthesis: arginase and transamidinase. These enzyme activities were studied in two human melanoma cell lines differing in their Km of diamine oxidase for putrescine and in their tumorigenicity in nude mice. Arginase activity accounts for the majority of ornithine formed in the highly tumorigenic cell line, while the majority of ornithine is derived from transamidinase action in the poorly tumorigenic cell line, with concomitant formation of methyl guanidine, a potent inhibitor of diamine oxidase. 相似文献
203.
Segmental flexibility of ribosomal protein S1 bound to ribosomes and Q beta-replicase 总被引:1,自引:0,他引:1
The protonization pattern of the endogenous donor component D1 which feeds electrons directly into chl-a+II has been analyzed in Tris-washed inside-out thylakoids with the aid of appropriate pH-indicators. It was found that under repetitive flash excitation the amount of protons released is proportional to the extent of D1-oxidation, depending on the time between the flashes. The kinetics of D1-oxidation (being practically the same as in normal Tris-washed chloroplasts) are faster than the proton release by two orders of magnitude. The results lead to the conclusion that D1 is protonized in the reduced state with pK(Dox1) < 5 and becomes deprotonized in the oxidized state with pK(Dred1) ? 8. The proton release is kinetically limited by a transport barrier. Implications on the interpretation of the proton release pattern in preparation with intact water oxidation are discussed. 相似文献
204.
205.
Janis E. Lochner Geoffrey V. F. Seaman Philip Blume Arthur Malley 《Cell biochemistry and biophysics》1982,4(1):15-24
Concanavalin A, at extremely low concentrations, will produce significant increases in the electrophoretic mobility of murine
splenic T lymphocytes. It has been established that the alteration in cellular surface charge is mediated by a factor produced
by those lymphocytes that have reacted directly with con A. We originally conjectured that the mobility change might be the
consequence of an alteration in the distribution of the charged moieties of membrane glycoproteins. The results of experiments
conducted at low temperature raise some questions about this mechanism. Further experiments have been performed to establish
the nature of the physicochemical alterations in the peripheral zone of the factor-stimulated lymphocytes that are manifest
as changes in cellular surface charge. The results of these studies indicate that, subsequent to the interaction of T lymphocytes
with con A, there is a reduction in the number of positively charged amino groups effective at the electrophoretic surface
of the cells. 相似文献
206.
C. A. Burga 《Plant Ecology》1982,49(3):173-186
In the first part, an overview of the history of palynological researeh in Switzerland and particularly in the Grisons is given, with a map showing all investigated areas in the Grisons. The second part deals with the significance of the pollenanalytical research in the Grisons, namely, the history of vegetation during the Late and Post Glacial, climatic fluctuations and applications in geomorphology, archaeology and forestry research. Finally, some results concerning the history of vegetation during the Late and Post Glacial are discussed.I would like to thank my colleague H. Holzhauser for his help with the drawing of the figures. 相似文献
207.
James C. Fuscoe J.Patrick ONeill Richard Machanoff Abraham W. Hsie 《Mutation research》1982,96(1):15-30
We describe an assay for the quantification of reverse mutations at the hypoxanthine-guanine phosphoribosyltransferase (hgprt) locus in Chinese hamster ovary cells utilizing the selective agent L-azaserine (AS). Conditions are defined in terms of optimal AS concentration, cell density, and phenotypic expression time. After treatment, replicate cultures of 106 cells are allowed a 48-h phenotypic expression time in 100-mm plates. AS (10 μM) is then added directly to the growing culture and AS-resistant (ASr) cells form visible colonies. This assay is used to quantify ICR-191-, ICR-170-, and N-ethyl-N-nitrosourea-induced reversion of independently isolated HGPRT? clones. The ASr phenotype is characterized both physiologically and biochemically. All ASr clones isolated are stably resistant to AS and aminopterin but sensitive to 6-thioguanine. They also have re-expressed HGPRT enzyme. In addition, several revertants are shown to contain altered HGPRT. The data provide further evidence that ICR-191 and ICR-170 cause structural gene mutations in mammalian cells and also suggest that ICR-191, ICR-170, and N-ethyl-N-nitrosourea induce similar types of mutations in Chinese hamster ovary cells. 相似文献
208.
The cytotoxic and mutagenic effect of (±)-7β,8α-dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (anti BPDE) in normally excision diploid human cells treated just prior to onset of S was compared with that of cells allowed ~ 16 h for excision repair before onset of S and with that observed in excision-deficient serodema pigmentosum (SP12BE) cells. The cells were synchronized by release from density inhibition of cell replication. DNA synthesis began ~ 22 h after the cells were plated at lower density (i.e., 1.4 × 104 cells/cm2). The frequency of thioguanine-resistant mutants induced in normal cells treated just prior to onset of S was ~ 12- to 16-fold higher than that observed in cells treated in early G1 or treated in G0 (confluence) and then plated at lower density. The frequency approximated that expected for XP12BE cells from extrapolation of data obtained at lower doses. The frequency of mutants measured in normal cells treated in exponential growth was also much higher than that in the cells treated in early G1 or in G0, No such difference could be seen in XP12BE cells treated in exponential growth or in G0. In contrast to the mutagenicity data in the normal cells, there was no significant difference in the slope of the survival curve of normal cells treated at various times prior to S phase at low densities. However, normal cells treated even at the onset of S exhibited survival equal to XP12BE cells give a 4- to 5-fold lower dose. The data support the hypothesis that DNA synthesis is the cellular event which converts unexcised DNA lesions into mutations. However, they indicate that S is not the event primarily responsible for translating DNA damage into cell death. Accompanying studies on the rate of excision of anti BPDE adducts from the normal cells during the period priot to S support the conclusions. 相似文献
209.
Pregnenolone (3β-hydroxy-5-pregnen-20-one) and DHA (3β-hydroxy-5-androsten-17-one), substrates for 3β-hy-droxysteroid dehydrogenase (3β-HSD), with KM values of 15–40 nM, were ineffective inhibitors of 5-ene-3-ketosteroid isomerase (isomerase), with KI values >40 μM in each case. Progesterone and androstenedione (4-androstene-3, 17-dione), 3β-HSD inhibitors with KI values of 5.0 μM and 0.8 μM respectively, were also relatively ineffective inhibitors of isomerase, with KI values of 30 μM and 16.5 μM respectively. Exposure of microsomes to hydrogen peroxide, which significantly increases the KM for pregnenolone as a 3β-HSD substrate, had no effect on the KM for the isomerase substrate 5-pregnene-3, 20-dione.It is concluded that the data do not support the common site concept with regard to the conversion of pregnenolone to progesterone by human placental microsomes. 相似文献
210.
Do benzodiazepines bind at adenosine uptake sites in CNS? 总被引:6,自引:0,他引:6
Benzodiazepines inhibit adenosine uptake into rat cerebral cortical synaptosomes and their potency as inhibitors of adenosine uptake is closely correlated with therapeutic efficacy. Agents which possess “benzodiazepine like” activities such as CL218,872, zopiclone and fominoben and which displace benzodiazepine binding to brain cell membranes, are also inhibitors of adenosine uptake into brain synaptosomes. The IC50 values of all these compounds as inhibitors of adenosine uptake are in close agreement with the IC50 values obtained for the displacement of benzodiazepine binding to the brain receptors. Adenosine uptake inhibitors (dipyridamole, hexobendine, papaverine, 6-(2-hydroxy-5-nitrobenzyl)thioguanosine) which competitively inhibit adenosine uptake, presumably by blocking adenosine binding to its carrier-protein, are competitive inhibitors of diazepam binding to the brain membrane receptors. The finding of a pronounced correlation between inhibition of benzodiazepine binding and inhibition of adenosine uptake further supports the proposal that benzodiazepines may exert part of their pharmacological action through the inhibition of adenosine uptake. 相似文献