全文获取类型
收费全文 | 570182篇 |
免费 | 56825篇 |
国内免费 | 1142篇 |
专业分类
628149篇 |
出版年
2018年 | 17240篇 |
2017年 | 16161篇 |
2016年 | 14109篇 |
2015年 | 9129篇 |
2014年 | 9771篇 |
2013年 | 13581篇 |
2012年 | 20531篇 |
2011年 | 30528篇 |
2010年 | 24320篇 |
2009年 | 19829篇 |
2008年 | 25223篇 |
2007年 | 27818篇 |
2006年 | 13056篇 |
2005年 | 14181篇 |
2004年 | 13630篇 |
2003年 | 13263篇 |
2002年 | 12485篇 |
2001年 | 22024篇 |
2000年 | 22087篇 |
1999年 | 17521篇 |
1998年 | 6390篇 |
1997年 | 6607篇 |
1996年 | 6413篇 |
1995年 | 5799篇 |
1994年 | 5854篇 |
1993年 | 5696篇 |
1992年 | 13742篇 |
1991年 | 13088篇 |
1990年 | 12718篇 |
1989年 | 12588篇 |
1988年 | 11247篇 |
1987年 | 10871篇 |
1986年 | 9939篇 |
1985年 | 9713篇 |
1984年 | 8276篇 |
1983年 | 7173篇 |
1982年 | 5623篇 |
1981年 | 5103篇 |
1980年 | 4746篇 |
1979年 | 7743篇 |
1978年 | 5970篇 |
1977年 | 5469篇 |
1976年 | 5114篇 |
1975年 | 5406篇 |
1974年 | 5847篇 |
1973年 | 5696篇 |
1972年 | 5729篇 |
1971年 | 5327篇 |
1970年 | 3943篇 |
1969年 | 3860篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Intramolecularly hydrogen-bonded peptide conformations 总被引:1,自引:0,他引:1
C Toniolo 《CRC critical reviews in biochemistry》1980,9(1):1-44
Over the past few years the possible occurrence of intramolecularly hydrogen-bonded structures in linear and cyclic peptides has attracted increasing attention. In this review emphasis is given to solid-state studies, particularly by X-ray diffraction and infrared absorption techniques. Conformational energy calculations are also considered. The discussion is focused both on model peptides and biological activity polypeptide molecules. The tetrapeptide system (Formula: see text), examined allows one to discuss the extended C5 structure and the various folded conformations, namely the C7 (gamma-turn), C8, C10 (beta-turn), C11, and C13 conformations. The four latter forms may include cis peptide configurations. The oxy-analogs to the C7, C10, and C13 conformations and structures containing bifurcated hydrogen bonds are also discussed. The last sections describe intramolecularly hydrogen-bonded peptide structures involving: (1) a side-chain group, (2) the N-protecting group (in synthetic model compounds), and (3) a beta-amino acid. 相似文献
992.
Tihomir Todorov Albena Todorova Bilyana Georgieva Vanyo Mitev 《Molecular biotechnology》2010,45(2):150-154
We report on a unified rapid betaine-based-PCR protocol for amplification of the (CAG)n region in Huntington disease (HD) and the (CGG)n region in Fragile X syndrome (FXS), followed by an electrophoretic separation on automated sequencer for precise determination
of the triplet numbers. The high betaine concentration (2.5 M betaine) permits precise amplification of the CAG and CGG repeats.
Ten HD affected patients and 10 healthy individuals from HD families were re-evaluated. For FXS the CGG region in normal individuals
and premutations of about 100 repeats were precisely amplified by this protocol. Ten unrelated FXS premutation carriers and
24 mentally retarded non-FXS affected boys were re-examined by this method. The results totally coincided with the previous
ones. This protocol is a good choice as a fast screening test. Within 24 h we can have preliminary information on the patient’s
genetic status. Normal individuals, CGG premutation carriers up to 100 repeats, as well as HD patients carrying an expansion
up to 50 CAG repeats can be easily clarified. This accounts for a relatively large proportion (about 90%) of the suspected
HD and FXS patients, referred to our laboratory for genetic analysis. The calculation of the repeat’s number is more accurate
for the correct interpretation of the results, screening tests and genetic counselling. 相似文献
993.
994.
SUMMARY. The input of terrestrial invertebrates from different tree canopies to a trout stream was determined for a 28-week period from April to October, 1980. Sycamore produced the greatest number of animals, followed by oak and alder. Ash was not significantly different from the controls. Coleoptera, Diptera, Homoptera and Arachnida made up the greatest number of animals caught, with Lepidoptera larvae important beneath oak. The input of biomass (g m-2 dry wt) was also greatest beneath sycamore (35.80), followed by oak (27.76), alder (20.39), ash (11.15) and control (9.92). The input of biomass was bimodal. The significance of terrestrial invertebrates as food for salmonids is discussed. 相似文献
995.
Glycine transporter from rat brain stem and spinal cord is inactivated by specific sulfhydryl reagents. Modification of lysine residues also promotes a decrease of the transporter activity but in a lesser extent than that promoted by thiol group reagents. Mercurials showed a more marked inhibitory effect than maleimide derivatives. SH groups display a similar reactivity for p-chloromercuribenzenesulfonate (pCMBS) and mersalyl in synaptosomal membrane vesicles and proteoliposomes reconstituted with the solubilized transporter. However, different reactivity is observed with N-ethylmaleimide (MalNEt), the greatest effect being attained in membrane vesicles. The rate of inactivation by pCMBS and MalNEt is pseudo-first-order showing time- and concentration-dependence. pCMBS and MalNEt decrease the Vmax for glycine transport and to a lesser extent act on the apparent Km. Treatment with dithiothreitol (DTT) of the transporter modified by pCMBS results in a complete restoration of transporter activity indicating that the effect exercised by the reagent is specific for cysteine residues on the protein. It is concluded that SH groups are involved in the glycine transporter function and that these critical residues are mostly located in a relatively hydrophilic environment of the protein. 相似文献
996.
Kinetics of RNA replication 总被引:4,自引:0,他引:4
997.
998.
999.
1000.