全文获取类型
收费全文 | 12680篇 |
免费 | 568篇 |
国内免费 | 538篇 |
专业分类
13786篇 |
出版年
2023年 | 66篇 |
2022年 | 98篇 |
2021年 | 132篇 |
2020年 | 178篇 |
2019年 | 233篇 |
2018年 | 279篇 |
2017年 | 180篇 |
2016年 | 204篇 |
2015年 | 205篇 |
2014年 | 521篇 |
2013年 | 689篇 |
2012年 | 408篇 |
2011年 | 488篇 |
2010年 | 396篇 |
2009年 | 493篇 |
2008年 | 562篇 |
2007年 | 648篇 |
2006年 | 606篇 |
2005年 | 619篇 |
2004年 | 454篇 |
2003年 | 408篇 |
2002年 | 330篇 |
2001年 | 227篇 |
2000年 | 216篇 |
1999年 | 201篇 |
1998年 | 204篇 |
1997年 | 196篇 |
1996年 | 199篇 |
1995年 | 180篇 |
1994年 | 181篇 |
1993年 | 143篇 |
1992年 | 157篇 |
1991年 | 142篇 |
1990年 | 140篇 |
1989年 | 143篇 |
1988年 | 111篇 |
1987年 | 134篇 |
1986年 | 111篇 |
1985年 | 271篇 |
1984年 | 445篇 |
1983年 | 337篇 |
1982年 | 354篇 |
1981年 | 341篇 |
1980年 | 258篇 |
1979年 | 240篇 |
1978年 | 196篇 |
1977年 | 161篇 |
1976年 | 101篇 |
1975年 | 63篇 |
1973年 | 50篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
Zorbas YG Kakurin VJ Denogradov SD Luzhkov SH Neofitov AC 《Biological trace element research》2002,90(1-3):155-173
Hypokinesia (diminished movement) induces muscle mineral depletion. However, the mechanism of muscle mineral depletion during
hypokinesia (HK) remains unknown. Measuring electrolyte retention and electrolyte values in muscle, plasma, and urine during
and after HK, the aim of this study was to discover if HK could depress mineral retention and lead to muscle mineral depletion.
Studies were done on 204 13-wk-old male Wistar rats (370–390 g) during 10 d pre-HK period, 98 d HK period, and 15 d post-HK
period. Rats were equally divided into two groups: vivarium control rats (VCR) and hypokinetic rats (HKR). All hypokinetic
rats were kept for 98 d in small individual cages, which restricted their movements in all directions without hindering food
and water intakes. All control rats were housed for 98 d in individual cages under vivarium control conditions. Both groups
of rats were pair-fed.
During the HK period skeletal muscle sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), and water content and electrolyte
retention decreased significantly (p < 0.05), while urinary and plasma electrolyte levels increased significantly (p < 0.05) in HKR compared with their pre-HK values and their respective VCR. During the initial days of the post-HK period,
mineral retention increased significantly (p < 0.05), plasma and urinary electrolyte level decreased significantly (p < 0.05), while muscle electrolyte and water content remained significantly (p < 0.05) depressed in HKR compared with VCR. Muscle mineral and water content, electrolyte retention, plasma, and urinary
electrolyte values did not change in VCR compared with their pre-HK values.
It was concluded that during HK decreased muscle mineral content may suggest muscle mineral depletion, while increased urinary
electrolyte loss and muscle mineral depletion may demonstrate reduced mineral retention. Reduced electrolyte excretion and
depressed muscle mineral content during post-HK may indicate skeletal muscle mineral depletion during HK. Dissociation between
electrolyte retention and muscle mineral depletion may demonstrate the presence of decreased electrolyte retention as the
mechanism of muscle electrolyte depletion during prolonged HK. 相似文献
972.
We examined pyrethroid resistant Mexican strains of Boophilus microplus using biochemical and molecular tests to determine the mechanisms conferring resistance. Permethrin hydrolysis assays and
esterase activity gels indicated enhanced esterase-mediated metabolic detoxification in the Cz strain, while one other pyrethroid
resistant strain, SF, and two pyrethroid susceptible strains had lower levels of permethrin hydrolysis. Results from assays
using a PCR-based test to detect a pyrethroid target site resistance-associated mutation in the tick sodium channel gene found
only low levels of mutations in the Cz strain, while the SF strain had a high level of the mutated sodium channel alleles.
A specific esterase, designated CzEst9, believed to be responsible for the esterase-mediated pyrethroid resistance in the
Cz strain was purified, and the gene encoding CzEst9 cloned.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
973.
Bellin R Capila I Lincecum J Park PW Reizes O Bernfield MR 《Glycoconjugate journal》2002,19(4-5):295-304
Heparan sulfate proteoglycans are known to modulate the activity of a large number of extracellular ligands thereby having the potential to regulate a great diversity of biological processes. The long-term studies in our laboratory have focused on the syndecans, one of the major cell surface heparan sulfate proteoglycan families. Most early work on syndecans involved biochemical studies that provided initial information on their structure and putative biological roles. In recent years, the development of transgenic organisms has allowed a more complete understanding of syndecan function. Studies with transgenic syndecan-1 and syndecan-3 mice have demonstrated an unforeseen role for syndecans in the regulation of feeding behavior. Syndecan-1 knockout mice display a reduced susceptibility to both Wnt-induced tumorigenesis and microbial pathogenesis. Experiments with Drosophila show that syndecan is first expressed upon cellularization in the early embryo, and may play a role in the early developmental stages of the fly. This review focuses on these diverse functions of the syndecans that have been elucidated by the use of transgenic mice and Drosophila as model systems. Published in 2003. 相似文献
974.
975.
Nishigaki R Shinohara T Toda T Omori A Ichinose S Itoh M Shirayoshi Y Kurimasa A Oshimura M 《Biochemical and biophysical research communications》2002,295(1):112-118
An extra copy of human chromosome 21 (Chr 21) causes Down syndrome (DS), which is characterized by mental retardation and congenital heart disease (CHD). Chimeric mice containing Chr 21 also exhibit phenotypic traits of DS including CHD. In this study, to identify genes contributing to DS phenotypes, we compared the overall protein expression patterns in hearts of Chr 21 chimeras and wild type mice by two-dimensional electrophoresis. The endogenous mouse atrial specific isoform of myosin light chain-2 (mlc-2a) protein was remarkably downregulated in the hearts of chimeric mice. We also confirmed that the human MLC-2A protein level was significantly lower in a human DS neonate heart, as compared to that of a normal control. Since mouse mlc-2a is involved in heart morphogenesis, our data suggest that the downregulation of this gene plays a crucial role in the CHD observed in DS. The dosage imbalance of Chr 21 has a trans-acting effect which lowers the expression of other genes encoded elsewhere in the genome. 相似文献
976.
We measured the effect of the intercalating oxazole yellow DNA dye quinolinium,4-[(3-methyl-2(3H)-benzoxazolylidene)methyl]-1-[3-(trimethylammonio)propyl]-,diiodide (YO-PRO) and its homodimer (YOYO) on the melting of self-complementary DNA duplexes using a gel-based assay. The assay, which requires a self-complementary DNA sequence, is independent of the optical properties of the molecules in solution. The melting temperature of the DNA is observed to increase in direct proportion to the number of occupied intercalation sites on the DNA, irrespective of whether the dye molecules are in monomer or dimer form. The increase is approximately 2.5 degrees C for each intercalation site occupied in the presence of 38 mM [Na(+)], for dye/duplex ratios in which less than 1/5 of the available intercalation sites are occupied. 相似文献
977.
Proteome analysis of hepatocellular carcinoma 总被引:26,自引:0,他引:26
Lim SO Park SJ Kim W Park SG Kim HJ Kim YI Sohn TS Noh JH Jung G 《Biochemical and biophysical research communications》2002,291(4):1031-1037
Development of hepatocellular carcinoma (HCC) is a complex process involving multiple changes in gene expression and usually occurs in the presence of liver cirrhosis. In this research, we observed proteome alterations of three tissue types isolated from livers of HCC patients: normal, cirrhotic, and tumorous tissue. Proteome alterations were observed using two-dimensional polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Comparing the tissue types with each other, a significant change in expression level was found in 21 proteins. Of these proteins, sarcosine dehydrogenase, liver carboxylesterase, peptidyl-prolyl isomerase A, and lamin B1 are considered novel HCC marker candidates. In particular, lamin B1 may be considered as a marker for cirrhosis, because its expression level changes considerably in cirrhotic tissue compared with normal tissue. The proteins revealed in this experiment can be used in the future for studies pertaining to hepatocarcinogenesis, or as diagnostic markers and therapeutic targets for HCC. 相似文献
978.
Jun?Keun?ChangEmail author Yun?Seok?Heo Hyunwoo?Bang Keunchang?Cho Seok?Chung Chanil?Chung Dong?Chul?Han 《Biotechnology and Bioprocess Engineering》2003,8(4):233-239
For the quantitative analysis of an unknown sample a calibration curve should be obtained, as analytical instruments give
relative, rather than absolute measurements. Therefore, researchers should make standard samples with various known concentrations,
measure each standard and the unknown sample, and then determine the concentration of the unknown by comparing the measured
value to those of the standards. These procedures are tedious and time-consuming. Therefore, we developed a polymer based
microfluidic device from polydimethylsiloxane, which integrates serial dilution and capillary electrophoresis functions in
a single device. The integrated microchip can provide a one-step analytical tool, and thus replace the complex experimental
procedures. Two plastic syringes, one containing a buffer solution and the other a standard solution, were connected to two
inlet holes on a microchip, and pushed by a hydrodynamic force. The standard sample is serially diluted to various concentrations
through the microfluidic networks. The diluted samples are sequentially introduced through microchannels by electro-osmotic
force, and their laser-induced fluorescence signals measured by capillary electrophoresis. We demonstrate the integrated microchip
performance by measuring the fluorescence signals of fluorescein at various concentrations. The calibration curve obtained
from the electropherograms showed the expected linearity. 相似文献
979.
Goh YL Yasin R Puthucheary SD Koh YT Lim VK Taib Z Thong KL 《Journal of applied microbiology》2003,95(5):1134-1142
AIMS: DNA fingerprinting of Salmonella enterica serotype Paratyphi B isolated in Malaysia during 1982-83, 1992 and 1996-2002 was carried out by pulsed-field gel electrophoresis (PFGE), antimicrobial susceptibility tests and D-tartrate utilization tests to assess the extent of genetic diversity of these isolates in Malaysia. METHODS AND RESULTS: Eighty-six human isolates and one food isolate of Salm. Paratyphi B were analysed by PFGE, antimicrobial susceptibility tests and D-tartrate utilization tests. Sixty-five strains were D-tartrate-negative (dT-) while 22 strains were D-tartrate-positive (dT+). Thirty-seven per cent of the Salm. Paratyphi B strains were resistant to one or more antimicrobial agents. PFGE analysis clearly distinguished the dT- and dT+ strains into two clusters based on the unweighted pair group average method (UPGMA). Twenty-two XbaI-pulsotypes were observed among the 65 dT- strains while 17 XbaI-pulsotypes were observed among the 22 isolates of Salm. Paratyphi B dT+. CONCLUSIONS: The present study showed that PFGE was very discriminative with 33.7% of the strains yielding distinct fingerprints. Paratyphoid fever in Malaysia is probably caused by one predominant, endemic clone of Salm. Paratyphi B dT- with various subtypes. There was no association between the pulsotypes and the severity of the disease indicating that the severity of the disease is probably multifactorial. SIGNIFICANCE AND IMPACT OF THE STUDY: The findings of the present study verify the usefulness of PFGE in characterizing strains of Salm. Paratyphi B. This is the first report on the application of PFGE on a large collection of Salm. Paratyphi B in Malaysia. 相似文献
980.
Abstract
Sea cucumbers possess a peculiar specialized defense system: the so-called Cuvierian tubules. The system is mobilized when
the animal is mechanically stimulated, resulting in the discharge of a few white filaments, the tubules. Their great adhesivity,
combined with their high tensile strength, allows Cuvierian tubules to entangle and immobilize potential predators. The cellular
origin and composition of the Cuvierian tubule adhesive were investigated in the species Holothuria forskali by studying prints left on the substratum after mechanical detachment of the tubule. Polyclonal antibodies raised against
tubule print material were used to locate the origin of tubule print constituents in the tubules. Extensive immunoreactivity
was detected in the secretory granules of mesothelial granular cells, suggesting that their secretions make up the bulk of
the adhesive material. Tubule print material consists of 60% proteins and 40% carbohydrates, a composition that is unique
among the adhesive secretions of marine invertebrates. Although it is highly insoluble, a small fraction of this material
can be extracted using denaturing buffers. Electrophoretic analysis of the extracts revealed that it contains about 10 proteins
with apparent molecular masses ranging from 17 to 220 kDa and with closely related amino acid compositions, rich in acidic
and in small side-chain amino acids. The adhesive from the Cuvierian tubules of H. forskali shares these characteristics with many marine bioadhesives and structural biomaterials. 相似文献