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921.
Coulomb blockade and the Kondo effect in single-atom transistors 总被引:7,自引:0,他引:7
Park J Pasupathy AN Goldsmith JI Chang C Yaish Y Petta JR Rinkoski M Sethna JP Abruña HD McEuen PL Ralph DC 《Nature》2002,417(6890):722-725
Using molecules as electronic components is a powerful new direction in the science and technology of nanometre-scale systems. Experiments to date have examined a multitude of molecules conducting in parallel, or, in some cases, transport through single molecules. The latter includes molecules probed in a two-terminal geometry using mechanically controlled break junctions or scanning probes as well as three-terminal single-molecule transistors made from carbon nanotubes, C(60) molecules, and conjugated molecules diluted in a less-conducting molecular layer. The ultimate limit would be a device where electrons hop on to, and off from, a single atom between two contacts. Here we describe transistors incorporating a transition-metal complex designed so that electron transport occurs through well-defined charge states of a single atom. We examine two related molecules containing a Co ion bonded to polypyridyl ligands, attached to insulating tethers of different lengths. Changing the length of the insulating tether alters the coupling of the ion to the electrodes, enabling the fabrication of devices that exhibit either single-electron phenomena, such as Coulomb blockade, or the Kondo effect. 相似文献
922.
VEGF regulates haematopoietic stem cell survival by an internal autocrine loop mechanism 总被引:49,自引:0,他引:49
Gerber HP Malik AK Solar GP Sherman D Liang XH Meng G Hong K Marsters JC Ferrara N 《Nature》2002,417(6892):954-958
Vascular endothelial growth factor (VEGF) is a principal regulator of blood vessel formation and haematopoiesis, but the mechanisms by which VEGF differentially regulates these processes have been elusive. Here we describe a regulatory loop by which VEGF controls survival of haematopoietic stem cells (HSCs). We observed a reduction in survival, colony formation and in vivo repopulation rates of HSCs after ablation of the VEGF gene in mice. Intracellularly acting small-molecule inhibitors of VEGF receptor (VEGFR) tyrosine kinase dramatically reduced colony formation of HSCs, thus mimicking deletion of the VEGF gene. However, blocking VEGF by administering a soluble VEGFR-1, which acts extracellularly, induced only minor effects. These findings support the involvement in HSC survival of a VEGF-dependent internal autocrine loop mechanism (that is, the mechanism is resistant to inhibitors that fail to penetrate the intracellular compartment). Not only ligands selective for VEGF and VEGFR-2 but also VEGFR-1 agonists rescued survival and repopulation of VEGF-deficient HSCs, revealing a function for VEGFR-1 signalling during haematopoiesis. 相似文献
923.
A receptor kinase gene regulating symbiotic nodule development 总被引:65,自引:0,他引:65
Leguminous plants are able to establish a nitrogen-fixing symbiosis with soil bacteria generally known as rhizobia. Metabolites exuded by the plant root activate the production of a rhizobial signal molecule, the Nod factor, which is essential for symbiotic nodule development. This lipo-chitooligosaccharide signal is active at femtomolar concentrations, and its structure is correlated with host specificity of symbiosis, suggesting the involvement of a cognate perception system in the plant host. Here we describe the cloning of a gene from Medicago sativa that is essential for Nod-factor perception in alfalfa, and by genetic analogy, in the related legumes Medicago truncatula and Pisum sativum. The identified 'nodulation receptor kinase', NORK, is predicted to function in the Nod-factor perception/transduction system (the NORK system) that initiates a signal cascade leading to nodulation. The family of 'NORK extracellular-sequence-like' (NSL) genes is broadly distributed in the plant kingdom, although their biological function has not been previously ascribed. We suggest that during the evolution of symbiosis an ancestral NSL system was co-opted for transduction of an external ligand, the rhizobial Nod factor, leading to development of the symbiotic root nodule. 相似文献
924.
Lincoln AJ Wickramasinghe D Stein P Schultz RM Palko ME De Miguel MP Tessarollo L Donovan PJ 《Nature genetics》2002,30(4):446-449
In a wide variety of animal species, oocyte maturation is arrested temporarily at prophase of meiosis I (ref. 1). Resumption of meiosis requires activation of cyclin-dependent kinase-1 (CDK1, p34cdc2), one component of maturation-promoting factor (MPF). The dual specificity phosphatases Cdc25a, Cdc25b and Cdc25c are activators of cyclin-dependent kinases; consequently, they are postulated to regulate cell-cycle progression in meiosis and mitosis as well as the DNA-damage response. We generated Cdc25b-deficient (Cdc25b-/-) mice and found that they are viable. As compared with wildtype cells, fibroblasts from Cdc25b-/- mice grew vigorously in culture and arrested normally in response to DNA damage. Female Cdc25b-/- mice were sterile, and Cdc25b-/- oocytes remained arrested at prophase with low MPF activity. Microinjection of wildtype Cdc25b mRNA into Cdc25b-/- oocytes caused activation of MPF and resumption of meiosis. Thus, Cdc25b-/- female mice are sterile because of permanent meiotic arrest resulting from the inability to activate MPF. Cdc25b is therefore essential for meiotic resumption in female mice. Mice lacking Cdc25b provide the first genetic model for studying the mechanisms regulating prophase arrest in vertebrates. 相似文献
925.
Germline mutations in FH predispose to dominantly inherited uterine fibroids, skin leiomyomata and papillary renal cell cancer 总被引:26,自引:0,他引:26
Tomlinson IP Alam NA Rowan AJ Barclay E Jaeger EE Kelsell D Leigh I Gorman P Lamlum H Rahman S Roylance RR Olpin S Bevan S Barker K Hearle N Houlston RS Kiuru M Lehtonen R Karhu A Vilkki S Laiho P Eklund C Vierimaa O Aittomäki K Hietala M Sistonen P Paetau A Salovaara R Herva R Launonen V Aaltonen LA;Multiple Leiomyoma Consortium 《Nature genetics》2002,30(4):406-410
926.
Protecting against promiscuity: the regulatory role of insulators 总被引:11,自引:0,他引:11
927.
The superoxide-generating NADPH oxidase: structural aspects and activation mechanism 总被引:31,自引:0,他引:31
Vignais PV 《Cellular and molecular life sciences : CMLS》2002,59(9):1428-1459
Flavocytochrome b
558
is the catalytic core of the respiratory-burst oxidase, an enzyme complex that catalyzes the NADPH-dependent reduction of
O2 into the superoxide anion O2
- in phagocytic cells. Flavocytochrome b
558
is anchored in the plasma membrane. It is a heterodimer that consists of a large glycoprotein gp91phox (phox for phagocyte oxidase) (β subunit) and a small protein p22phox (α subunit). The other components of the respiratory-burst oxidase are water-soluble
proteins of cytosolic origin, namely p67phox, p47phox, p40phox and Rac. Upon cell stimulation, they assemble with the membrane-bound
flavocytochrome b
558
which becomes activated and generates O2
-. A defect in any of the genes encoding gp91phox, p22phox, p67phox or p47phox results in chronic granulomatous disease, a
genetic disorder characterized by severe and recurrent infections, illustrating the role of O2
- and the derived metabolites H2O2 and HOCl in host defense against invading microorganisms. The electron carriers, FAD and hemes b, and the binding site for NADPH are confined to the gp91phox subunit of flavocytochrome b
558
. The p22phox subunit serves as a docking site for the cytosolic phox proteins. This review provides an overview of current
knowledge on the structural organization of the O2
--generating flavocytochrome b
558
, its kinetics, its mechanism of activation and the regulation of its biosynthesis. Homologues of gp91phox, called Nox and
Duox, are present in a large variety of non-phagocytic cells. They exhibit modest O2
--generating oxidase activity, and some act as proton channels. Their role in various aspects of signal transduction is currently
under investigation and is briefly discussed.
Received 28 May 2002; received after revision 20 June 2002; accepted 24 June 2002 相似文献
928.
Role of hydrogen peroxide and oxidative stress in healing responses 总被引:11,自引:0,他引:11
Rojkind M Domínguez-Rosales JA Nieto N Greenwel P 《Cellular and molecular life sciences : CMLS》2002,59(11):1872-1891
929.
Our understanding of how immune responses are generated and regulated drives the design of possible immunotherapies for cancer
patients. For that reason, we first describe briefly the actual immunological theories and their common perspectives about
cancer vaccine development. Second, we describe cancer vaccines that are able to induce tumor-specific immune responses in
cancer patients. However, these responses are not always followed by tumor rejection. At the end of the review, we discuss
two possible reasons that might explain this dichotomy of cancer immunology. First, the immune response generated, although
detectable, may not be quantitatively sufficient to reject the tumor. Second, the tumor microenvironment may modulate tumor
cell susceptibility to the systemic immune response induced by the immunization. Finally, we discuss what, in our opinion,
might be the best way to improve cancer vaccine strategies and how the relationship between the tumor and its surroundings
might be studied in more details.
Received 21 June 2001; received after revision 15 August 2001; accepted 15 August 2001 相似文献
930.
Cellular and molecular aspects of drugs of the future: meropenem 总被引:1,自引:0,他引:1
Cottagnoud P 《Cellular and molecular life sciences : CMLS》2002,59(11):1928-1933
Meropenem, first synthesized in the late eighties, has become one of the most important beta-lactam antibiotics of the carbapenem subclass used for the treatment of a variety of life-threatening infections. Due to its unique chemical structure, meropenem is not inactivated by the kidney dehydropeptidase I and the majority of microbial beta-lactamases. Its antimicrobial activity is based on its high affinity for the majority of cell wall-synthesizing enzymes, the so-called penicillin-binding proteins, of Gram-positive and -negative bacteria. However, bacteria have evolved several approaches to resist meropenem: (i) by reducing the affinity of the penicillin-binding proteins for the antibiotics, (ii) by decreasing the permeability of the outer membrane of Gram-negative bacteria, (iii) by using efflux pumps, and (iv) by activating zinc-dependent carbapenemases. Meropenem has a low toxicity profile and, in contrast to imipenem, no central nervous system toxicity. 相似文献