全文获取类型
收费全文 | 2957篇 |
免费 | 292篇 |
出版年
2021年 | 34篇 |
2019年 | 23篇 |
2018年 | 24篇 |
2017年 | 25篇 |
2016年 | 47篇 |
2015年 | 102篇 |
2014年 | 114篇 |
2013年 | 113篇 |
2012年 | 151篇 |
2011年 | 159篇 |
2010年 | 91篇 |
2009年 | 96篇 |
2008年 | 104篇 |
2007年 | 107篇 |
2006年 | 88篇 |
2005年 | 102篇 |
2004年 | 93篇 |
2003年 | 133篇 |
2002年 | 92篇 |
2001年 | 99篇 |
2000年 | 91篇 |
1999年 | 72篇 |
1998年 | 39篇 |
1997年 | 34篇 |
1996年 | 29篇 |
1995年 | 35篇 |
1994年 | 26篇 |
1993年 | 40篇 |
1992年 | 65篇 |
1991年 | 61篇 |
1990年 | 58篇 |
1989年 | 65篇 |
1988年 | 43篇 |
1987年 | 51篇 |
1986年 | 46篇 |
1985年 | 67篇 |
1984年 | 34篇 |
1983年 | 34篇 |
1982年 | 26篇 |
1981年 | 34篇 |
1980年 | 22篇 |
1979年 | 34篇 |
1978年 | 30篇 |
1977年 | 41篇 |
1976年 | 22篇 |
1974年 | 22篇 |
1973年 | 20篇 |
1972年 | 24篇 |
1969年 | 21篇 |
1968年 | 20篇 |
排序方式: 共有3249条查询结果,搜索用时 15 毫秒
991.
Gap junctions and fluid flow response in MC3T3-E1 cells 总被引:2,自引:0,他引:2
Saunders M. M.; You J.; Trosko J. E.; Yamasaki H.; Li Z.; Donahue H. J.; Jacobs C. R. 《American journal of physiology. Cell physiology》2001,281(6):C1917
In thecurrent study, we examined the role of gap junctions in oscillatoryfluid flow-induced changes in intracellular Ca2+concentration and prostaglandin release in osteoblastic cells. Thiswork was completed in MC3T3-E1 cells with intact gap junctional communication as well as in MC3T3-E1 cells rendered communication deficient through expression of a dominant-negative connexin. Ourresults demonstrate that MC3T3-E1 cells with intact gap junctions respond to oscillatory fluid flow with significant increases in prostaglandin E2 (PGE2) release, whereas cellswith diminished gap junctional communication do not. Furthermore, wefound that cytosolic Ca2+ (Ca ) responsewas unaltered by the disruption in gap junctional communication and wasnot significantly different among the cell lines. Thus our resultssuggest that gap junctions contribute to the PGE2 but notto the Ca response to oscillatory fluid flow. Thesefindings implicate gap junctional intercellular communication (GJIC) inbone cell ensemble responsiveness to oscillatory fluid flow and suggestthat gap junctions and GJIC play a pivotal role in mechanotransduction mechanisms in bone. 相似文献
992.
Hyperglucagonemia in rats results in decreased plasma homocysteine and increased flux through the transsulfuration pathway in liver 总被引:3,自引:0,他引:3
Jacobs RL Stead LM Brosnan ME Brosnan JT 《The Journal of biological chemistry》2001,276(47):43740-43747
An elevated plasma level of homocysteine is a risk factor for the development of cardiovascular disease. The purpose of this study was to investigate the effect of glucagon on homocysteine metabolism in the rat. Male Sprague-Dawley rats were treated with 4 mg/kg/day (3 injections per day) glucagon for 2 days while control rats received vehicle injections. Glucagon treatment resulted in a 30% decrease in total plasma homocysteine and increased hepatic activities of glycine N-methyltransferase, cystathionine beta-synthase, and cystathionine gamma-lyase. Enzyme activities of the remethylation pathway were unaffected. The 90% elevation in activity of cystathionine beta-synthase was accompanied by a 2-fold increase in its mRNA level. Hepatocytes prepared from glucagon-injected rats exported less homocysteine, when incubated with methionine, than did hepatocytes of saline-treated rats. Flux through cystathionine beta-synthase was increased 5-fold in hepatocytes isolated from glucagon-treated rats as determined by production of (14)CO(2) and alpha-[1-(14)C]ketobutyrate from l-[1-(14)C]methionine. Methionine transport was elevated 2-fold in hepatocytes isolated from glucagon-treated rats resulting in increased hepatic methionine levels. Hepatic concentrations of S-adenosylmethionine and S-adenosylhomocysteine, allosteric activators of cystathionine beta-synthase, were also increased following glucagon treatment. These results indicate that glucagon can regulate plasma homocysteine through its effects on the hepatic transsulfuration pathway. 相似文献
993.
Tamir?Gonen Angus?C?Grey Marc?D?Jacobs Paul?J?Donaldson Joerg?KistlerEmail author 《BMC cell biology》2001,2(1):17
Background
Although MP20 is the second most highly expressed membrane protein in the lens its function remains an enigma. Putative functions for MP20 have recently been inferred from its assignment to the tetraspanin superfamily of integral membrane proteins. Members of this family have been shown to be involved in cellular proliferation, differentiation, migration, and adhesion. In this study, we show that MP20 associates with galectin-3, a known adhesion modulator. 相似文献994.
Sample preparation is still the most critical step in two-dimensional gel electrophoresis (2-DE), and needs to be optimized for each type of sample. To analyze the proteome of the medicinal plant Catharanthus roseus, we developed and evaluated a sequential solubilization procedure for the solubilization of proteins after precipitation in trichloroacetic acid and acetone. The procedure includes solubilization with a conventional urea buffer followed by a stronger solubilizing buffer containing thiourea. The sequential solubilization of the precipitated proteins results in very different spot patterns following 2-DE. The number of protein spots which could be detected in both samples of the sequential solubilization was only about 10% of the total number of spots. Compared to solubilization in a single step, the total number of spots that could be detected in the sequential solubilization procedure was increased by 52%. The method described is simple and is applicable to different types of plant tissue. 相似文献
995.
996.
Toivonen JM O'Dell KM Petit N Irvine SC Knight GK Lehtonen M Longmuir M Luoto K Touraille S Wang Z Alziari S Shah ZH Jacobs HT 《Genetics》2001,159(1):241-254
Mutations in mtDNA-encoded components of the mitochondrial translational apparatus are associated with diverse pathological states in humans, notably sensorineural deafness. To develop animal models of such disorders, we have manipulated the nuclear gene for mitochondrial ribosomal protein S12 in Drosophila (technical knockout, tko). The prototypic mutant tko(25t) exhibits developmental delay, bang sensitivity, impaired male courtship, and defective response to sound. On the basis of a transgenic reversion test, these phenotypes are attributable to a single substitution (L85H) at a conserved residue of the tko protein. The mutant is hypersensitive to doxycyclin, an antibiotic that selectively inhibits mitochondrial protein synthesis, and mutant larvae have greatly diminished activities of mitochondrial redox enzymes and decreased levels of mitochondrial small-subunit rRNA. A second mutation in the tko gene, Q116K, which is predicted to impair the accuracy of mitochondrial translation, results in the completely different phenotype of recessive female sterility, based on three independent transgenic insertions. We infer that the tko(25t) mutant provides a model of mitochondrial hearing impairment resulting from a quantitative deficiency of mitochondrial translational capacity. 相似文献
997.
Grain processing and nutrition 总被引:1,自引:0,他引:1
Whole grains provide a wide range of nutrients and phytochemicals that optimize health. Epidemiologic studies support the protectiveness of whole grain consumption for cardiovascular disease and cancer. Dietary guidance endorses increased whole grains in our diet. A crucial question remaining is the effect of processing of whole grains on their content of nutrients and phytochemicals. Although processing is often considered to be a negative attribute in nutrition, and some forms of processing reduce nutritional value, many factors support the importance of processing of grains to enhance grain consumption. First, whole grains as harvested are generally not consumed directly by humans but require some processing prior to consumption. While refining, that is, removal of the bran and the germ, reduces the nutrient content of grain, milling of grains otherwise concentrates desirable grain components and removes poorly digested compounds and contaminants. Cooking of grains generally increases digestibility of nutrients and phytochemicals. Studies in both animal models and humans support the notion that processed grains are often nutritionally superior to unprocessed grains, probably because of enhanced nutrient bioavailability in processed grains. Processing of grains also provides shelf-stable products that are convenient and good tasting for consumers. 相似文献
998.
Protein flexibility predictions using graph theory 总被引:6,自引:0,他引:6
Techniques from graph theory are applied to analyze the bond networks in proteins and identify the flexible and rigid regions. The bond network consists of distance constraints defined by the covalent and hydrogen bonds and salt bridges in the protein, identified by geometric and energetic criteria. We use an algorithm that counts the degrees of freedom within this constraint network and that identifies all the rigid and flexible substructures in the protein, including overconstrained regions (with more crosslinking bonds than are needed to rigidify the region) and underconstrained or flexible regions, in which dihedral bond rotations can occur. The number of extra constraints or remaining degrees of bond-rotational freedom within a substructure quantifies its relative rigidity/flexibility and provides a flexibility index for each bond in the structure. This novel computational procedure, first used in the analysis of glassy materials, is approximately a million times faster than molecular dynamics simulations and captures the essential conformational flexibility of the protein main and side-chains from analysis of a single, static three-dimensional structure. This approach is demonstrated by comparison with experimental measures of flexibility for three proteins in which hinge and loop motion are essential for biological function: HIV protease, adenylate kinase, and dihydrofolate reductase. 相似文献
999.
Fluorochrome C-banding ofPinus radiata andP. taeda metaphase chromosomes showed many pericentromeric DAPI bands and interstitial CMA bands inP. radiata, and centromeric and interstitial CMA bands inP. taeda. Giemsa C-band patterns differed between the species with centromeric bands inP. radiata but no consistent bands inP. taeda. A karyotype ofP. radiata was developed based on banding patterns that distinguished all but two of the 12 pairs of chromosomes. In situ hybridization (ISH) using probes for high-copy ribosomal DNA (rDNA) showed 10 pairs of 18S–25S sites and two pairs of 5S sites in both species. Most of the sites were interstitial or centromeric. 相似文献
1000.
Biofilms and biodiversity: an interactive exploration of aquatic microbial biotechnology and ecology
J A Frederick D Jacobs W R Jones 《Journal of industrial microbiology & biotechnology》2000,24(5):334-338
The study of biofilms provides a unique educational opportunity to examine ecosystems, biodiversity and applications of environmental
biotechnology. There are many variables that could be studied for measuring the interactions between bacterial biofilms and
invertebrate biodiversity as a method for assessing the health of aquatic ecosystems. These interactions also lend themselves
to an easily replicated model system which can be used to reach a wide audience with an educational opportunity for students
as well as a professional development opportunity for teachers. At the foundation of the research are invaluable basic microbiology
skills: strain collection, isolation, cultivation and characterization. Through the additional process of characterizing,
identifying and enumerating invertebrate organisms that attach to bacterial biofilms in aquatic ecosystems, there evolved
a multidisciplinary class laboratory activity that has found broad application. This activity is captivating not only to undergraduate
microbiology students but to middle and high school students and their teachers. The demand for information about the activity
has led to the development of a truly interactive web-based lesson, which in turn has resulted in additional inquiries and
further refinement of the lesson as an undergraduate independent research course. Both of these are freely accessible on the
web, with growing international participation and data exchange. Journal of Industrial Microbiology & Biotechnology (2000) 24, 334–338.
Received 19 April 1999/ Accepted in revised form 17 February 2000 相似文献