全文获取类型
收费全文 | 2978篇 |
免费 | 180篇 |
出版年
2023年 | 14篇 |
2022年 | 40篇 |
2021年 | 56篇 |
2020年 | 35篇 |
2019年 | 75篇 |
2018年 | 69篇 |
2017年 | 54篇 |
2016年 | 90篇 |
2015年 | 165篇 |
2014年 | 141篇 |
2013年 | 208篇 |
2012年 | 245篇 |
2011年 | 209篇 |
2010年 | 137篇 |
2009年 | 101篇 |
2008年 | 174篇 |
2007年 | 179篇 |
2006年 | 169篇 |
2005年 | 163篇 |
2004年 | 158篇 |
2003年 | 135篇 |
2002年 | 152篇 |
2001年 | 23篇 |
2000年 | 17篇 |
1999年 | 28篇 |
1998年 | 21篇 |
1997年 | 19篇 |
1996年 | 23篇 |
1995年 | 19篇 |
1994年 | 17篇 |
1993年 | 14篇 |
1992年 | 12篇 |
1991年 | 19篇 |
1990年 | 9篇 |
1989年 | 9篇 |
1988年 | 10篇 |
1987年 | 13篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 12篇 |
1983年 | 10篇 |
1982年 | 21篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 9篇 |
1978年 | 5篇 |
1977年 | 10篇 |
1976年 | 5篇 |
1972年 | 4篇 |
1971年 | 4篇 |
排序方式: 共有3158条查询结果,搜索用时 31 毫秒
31.
Summary X-inactivation patterns were studied by replication analyses both in lymphocytes and skin fibroblasts of two patients carrying balanced X-autosome translocations, t(X;10)-(pter;q11) and t(X;17)(q11;q11), and one patient with an unbalanced translocation t(X;22)(p21;q11). Preferential late replication of the normal X chromosome was found in lymphocytes of both patients carrying balanced translocations and in skin fibroblasts of the patient carrying the translocation t(X;17). However, skin fibroblasts of the patient with a translocation t(X;10) showed preferential late replication of the abnormal der(X) chromosome with no spreading of late replication to the autosomal segment. In the case of unbalanced translocation t(X;22) there was preferential late replication of the der(X) chromosome both in lymphocytes and skin fibroblasts. The abnormal phenotype of the patients is discussed in relation to the observed X-inactivation patterns and the variability of the patterns in different tissues. 相似文献
32.
Rino Cella Roberta Colombo Maria Grazia Galli Erik Nielsen Franco Rollo Francesco Sala 《Physiologia plantarum》1982,55(3):279-284
Rice ( Oryza sativa L.) cells returning to in vitro culture after preservation at superlow temperature in liquid nitrogen are characterized by a number of physiological alterations. These include: reduction in respiration and glucose uptake, loss of intracellular potassium, decrease in the cellular level of key metabolites (ATP, glucose-6-phosphate and pyruvate) and fragility of protoplasts following the action of cell wall-degrading enzymes.
Nevertheless, cell growth resumes after a short lag phase (2–4 days) with an actual 70–100% cell survival, thus indicating that the observed damage is not lethal and can be repaired in a short time. 相似文献
Nevertheless, cell growth resumes after a short lag phase (2–4 days) with an actual 70–100% cell survival, thus indicating that the observed damage is not lethal and can be repaired in a short time. 相似文献
33.
In the study of chemical modification of enzymes and other biologically active proteins, plots of fractional residual activity
as a function of number of groups modified per enzyme molecule are often used to establish a correlation between the chemical
modification and enzyme inactivation reactions and to determine the stoichiometry of the modification reaction. This paper
presents a critical examination of the underlying theoretical framework of such graphs. Whereas these plots are usually presented
as linear functions, it is shown here that the general equation describing the relationship between inactivation and modification
contains an exponential term; therefore, in the general case, the plot is actually a curve. It is suggested that caution be
exercised in the interpretation of such plots and that equations such as those derived in the text be used to fit theoretical
curves to the data, in order to maximize the information gained from chemical modification experiments. 相似文献
34.
Somatic embryoids differentiated in suspension cultures of G. klotzschianum after 3–4 weeks of culture in a liquid medium containing glutamine (optimally, 10–15 mM). Embryogenesis occurred after a preculture of callus on a medium containing 10 mg/l of the cytokinin, 2iP. The embryoids had meristematic regions, a well formed epidermis, and formed roots and vestigial leaves. Asparagine was much less effective than glutamine in promoting embryoid differentiation. The presence of 2,4-D in the medium resulted in increased vigor of the suspension cultures and subsequently in the formation of many embryoids, but does not seem to be necessary for somatic embryogenesis in cotton.Technical Article 14646 from the Texas Agricultural Experiment Station 相似文献
35.
36.
Enkephalin-binding systems in human plasma 总被引:1,自引:0,他引:1
Roberta Possenti Valeria De Marco Ornella Cherubini L. Giorgio Roda 《Neurochemical research》1983,8(4):423-432
Three amino acid-containing fractions present in human plasma are shown to bind both leu and met-enkephalin: serum albumin and two species of a much lower molecular weight, in all likelihood polypeptides. The amount of enkephalin associated with serum albumin seems comparatively smaller than that associated with the two low molecular weight systems. These systems jointly are apparently capable of binding a significant part of the circulating enkephalins. The possibility is suggested that the interactions described may play a role in maintaining the integrity of circulating enkephalins. 相似文献
37.
Orsola Tiboni Rita Cantoni Roberta Creti Piero Cammarano Anna Maria Sanangelantoni 《Journal of molecular evolution》1991,33(2):142-151
Summary The gene (fus) coding for elongation factor G (EF-G) of the extremely thermophilic eubacteriumThermotoga maritima was identified and sequenced. The EF-G coding sequence (2046 bp) was found to lie in an operon-like structure between the ribosomal protein S7 gene (rpsG) and the elongation factor Tu (EF-Tu) gene (tuf). TherpsG, fus, andtuf genes follow each other immediately in that order, which corresponds to the order of the homologous genes in thestr operon ofEscherichia coli. The derived amino acid sequence of the EF-G protein (682 residues) was aligned with the homologous sequences of other eubacteria, eukaryotes (hamster), and archaebacteria (Methanococcus vannielii). Unrooted phylogenetic dendrogram, obtained both from the amino acid and the nucleotide sequence alignments, using a variety of methods, lend further support to the notion that the (present) root of the (eu)bacterial tree lies betweenThermotoga and the other bacterial lineages. 相似文献
38.
Roberta Bertelli Fabrizio Ginevri Rosanna Gusmano Gian Marco Ghiggeri 《In vitro cellular & developmental biology. Animal》1991,27(10):799-804
Summary It has been suggested that the generation of toxic radicals plays an important role in toxicity by Adriamycin (ADR) on cancer
cell lines and in vivo. We have examined the role of free radicals in determining toxicity and resistance to ADR of rat glomerular
epithelial cells in culture; this method provides a good model for analyzing the mechanisms responsible for ADR experimental
nephrosis in rats. Three points were established: a) the intra- or extracellular site of ADR toxicity; b) the role of the
superoxide anion and of the hydroxyl radical in determining intra- and-extracellular cytotoxicity; and c) the implication
of oxido-reduction cycling as a potential route for ADR semiquinone transformation. Free ADR was found to induce the same
inhibition of [3H]thymidine incorporation into DNA as ADR bound to an agarose macroporous bed which prevents the intracellular incorporation
of the drug. Specific scavenging of free radical activity by the enzymes catalase and superoxide dismutase, the hydroxyl radical
inhibitors dimethyl sulfoxide and dimethylthiourea (DMTU) and by chelation of intracellular free iron with deferoxamine produced
only a partial restoration of [3H]thymidine incorporation into DNA, which was maximal for DMTU (30% of normal incorporation). DMTU treatment was unsuccessful
in preventing the extracellular cytostatic effect of ADR. Finally, glomerular epithelial cell killing (51Cr-release method) by 5-iminodaunorubicin, an ADR analogue with a modified quinone function that prohibits oxido-reduction
cycling, was higher than unmodified ADR. These results indicate that ADR may exert its cytotoxic effects on glomerular epithelial
cells by interaction at the cell surface, whereas the intracellular compartment, principally DNA, does not seem to be the
target of ADR effects. They also suggest that the free radicals are in part responsible for ADR intracellular cytotoxicity,
but other mechanisms should also be hypothesized. Finally, the participation of the ADR semiquinone radical in oxido-reduction
cycling seems not important for the induction of the cellular damage. 相似文献
39.
M Gemelli R Manganaro F De Luca C Imperatore G Costa C Mamì 《Hormones et métabolisme》1992,24(1):39-41
In order to clarify whether an interaction between endogenous opioids and feeding occurs at birth, we studied Beta-endorphin (beta-EP) and ACTH plasma levels in response to a feed of 10% glucose, or formula, in 120 healthy full-term infants. Neither postprandial beta-EP nor ACTH increases were found at the 24th hour or on the fourth day of life. beta-EP physiology in newborn infants seems to be different from adults. 相似文献
40.
A long-term experiment was performed with Branchiura sowerbyi in order to assess possible effects of LAS sorbed to sediment on its reproductive cycle, using concentrations in sediment 2–5 times higher than those calculated for the LC50 values of LAS dissolved in water. No significant effects were observed during the whole experiment, so that we can confirm that LAS adsorbed on sediment has a much lower influence on the examined animals than LAS dissolved in water. 相似文献