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911.
M. Geiser R. Schüpbach U. Waber P. Gehr 《Cellular and molecular life sciences : CMLS》1998,54(2):179-185
Attraction of lung macrophages to particle deposition sites has been demonstrated in different animal species. We reported
a threefold increase of the number of macrophages to occur within 40 min after polystyrene particle deposition in hamster
airways [Geiser et al. (1994) Am. J. Respir. Cell Mol. Biol. 160: 594–603]. Complement-derived chemotactic activity is one of the mechanisms postulated for macrophage recruitment. It was
the aim of this study to test whether complement-derived chemotactic activity is involved in the rapid recruitment of macrophages
to the site of deposited polystyrene particles in hamster airways. We first developed an in vitro cell migration assay for
hamster macrophages to assess complement-derived chemotaxis. Second, the bronchoalveolar lavage fluids (BALF) of four hamsters
that had inhaled aerosols of polystyrene microspheres were tested for chemotactic activity by this bioassay and compared with
BALF of four sham-exposed hamsters. Chemotactic response of macrophages was found toward complement-activated hamster serum,
whereas macrophage migration was not increased toward BALF of particle and sham-exposed hamsters. In contrast, macrophage
migration to BALF of both groups was reduced by 1.6-fold. Thus, the stimulus for macrophage recruitment to the site of deposited
polystyrene particles in hamster airways could not be demonstrated using this bioassay.
Received 10 September 1997; received after revision 24 November 1997; accepted 10 December 1997 相似文献
912.
On the origin of species by sympatric speciation. 总被引:49,自引:0,他引:49
Understanding speciation is a fundamental biological problem. It is believed that many species originated through allopatric divergence, where new species arise from geographically isolated populations of the same ancestral species. In contrast, the possibility of sympatric speciation (in which new species arise without geographical isolation) has often been dismissed, partly because of theoretical difficulties. Most previous models analysing sympatric speciation concentrated on particular aspects of the problem while neglecting others. Here we present a model that integrates a novel combination of different features and show that sympatric speciation is a likely outcome of competition for resources. We use multilocus genetics to describe sexual reproduction in an individual-based model, and we consider the evolution of assortative mating (where individuals mate preferentially with like individuals) depending either on an ecological character affecting resource use or on a selectively neutral marker trait. In both cases, evolution of assortative mating often leads to reproductive isolation between ecologically diverging subpopulations. When assortative mating depends on a marker trait, and is therefore not directly linked to resource competition, speciation occurs when genetic drift breaks the linkage equilibrium between the marker and the ecological trait. Our theory conforms well with mounting empirical evidence for the sympatric origin of many species. 相似文献
913.
Summary Judging by the physical and chemical properties and bacterial spectra, the antibiotic substance, Enniatin, previously isolated from a strain ofFusarium by the authors, appears to be identical with that which was recently reported byCook et al. derived from another strain and designated by them as Lateritiin-I, although the reported empirical formulæ differ. Numerous physical and chemical characteristics of Enniatin and its degradation products are given, and, further, two relatedFusarium antibiotics, here designated as Enniatin B and C, are briefly described.
Ausgeführt mit einem Beitrag aus den eidg. Arbeitsbeschaffungskrediten. 相似文献
Ausgeführt mit einem Beitrag aus den eidg. Arbeitsbeschaffungskrediten. 相似文献
914.
为了从分子水平上筛选肝细胞肝癌抗原,应用作者所在实验室创建的“重组克隆表达抗原的血清学鉴定技术”(SEREXserologicalindentificationofantigensbyrecombinantexpresioncloning)筛选人肝细胞肝癌(HCC)组织构建的cDNA文库,发现了许多与病人,自身血清高滴度抗体反应的克隆。应用多种异体(其他HCC病人,多种非HCC肿瘤病人,B型、C型病毒性肝炎病人,肝硬化病人以及健康人)血清反应分析表明,高滴度抗体反应多数出现在HCC病人。参照基因库寻找这些克隆的同源结构,发现其中许多抗原为至今未知基因所编码。进一步的血清和抗原分子分析将为HCC特异免疫治疗和诊断提供基础资料 相似文献
915.
R De Maria A Zeuner A Eramo C Domenichelli D Bonci F Grignani S M Srinivasula E S Alnemri U Testa C Peschle 《Nature》1999,401(6752):489-493
916.
917.
Attosecond metrology. 总被引:25,自引:0,他引:25
M Hentschel R Kienberger C Spielmann G A Reider N Milosevic T Brabec P Corkum U Heinzmann M Drescher F Krausz 《Nature》2001,414(6863):509-513
The generation of ultrashort pulses is a key to exploring the dynamic behaviour of matter on ever-shorter timescales. Recent developments have pushed the duration of laser pulses close to its natural limit-the wave cycle, which lasts somewhat longer than one femtosecond (1 fs = 10-15 s) in the visible spectral range. Time-resolved measurements with these pulses are able to trace dynamics of molecular structure, but fail to capture electronic processes occurring on an attosecond (1 as = 10-18 s) timescale. Here we trace electronic dynamics with a time resolution of = 150 as by using a subfemtosecond soft-X-ray pulse and a few-cycle visible light pulse. Our measurement indicates an attosecond response of the atomic system, a soft-X-ray pulse duration of 650 +/- 150 as and an attosecond synchronism of the soft-X-ray pulse with the light field. The demonstrated experimental tools and techniques open the door to attosecond spectroscopy of bound electrons. 相似文献
918.
919.
U. Zangemeister-Wittke R. A. Stahel 《Cellular and molecular life sciences : CMLS》1999,55(12):1585-1598
Small-cell lung cancer (SCLC) is characterized by its initial responsiveness to chemotherapy and the appearance of early metastases. Although combination chemotherapy, in some instances together with radiation, has improved the prognosis of this disease, in most patients SCLC ultimately recurs in a drug-resistant form. Several new strategies for the eradication of SCLC are being explored at the preclinical level. The identification of selective target molecules on the surface of SCLC cells, together with the progress made in antibody engineering, have provided new generations of antibodies and immunoconjugates as well as growth factor antagonists and inhibitors. In addition, recent advances in understanding the biology of SCLC have stimulated new investigations searching to counter the molecular basis underlying the increased proliferation and the apoptosis deficiency of SCLC cells. This can be achieved using antisense oligodeoxynucleotides that repress the expression of growth factor receptors and anti-apoptosis genes, or by gene replacement to compensate for the loss or inactivation of tumor suppressor genes. 相似文献
920.
Corrosion destroys more than three per cent of the world's GDP. Recently, the electrochemical decomposition of metal alloys has been more productively harnessed to produce porous materials with diverse technological potential. High-resolution insight into structure formation during electrocorrosion is a prerequisite for an atomistic understanding and control of such electrochemical surface processes. Here we report atomic-scale observations of the initial stages of corrosion of a Cu3Au111 single crystal alloy within a sulphuric acid solution. We monitor, by in situ X-ray diffraction with picometre-scale resolution, the structure and chemical composition of the electrolyte/alloy interface as the material decomposes. We reveal the microscopic structural changes associated with a general passivation phenomenon of which the origin has been hitherto unclear. We observe the formation of a gold-enriched single-crystal layer that is two to three monolayers thick, and has an unexpected inverted (CBA-) stacking sequence. At higher potentials, we find that this protective passivation layer dewets and pure gold islands are formed; such structures form the templates for the growth of nanoporous metals. Our experiments are carried out on a model single-crystal system. However, the insights should equally apply within a crystalline grain of an associated polycrystalline electrode fabricated from many other alloys exhibiting a large difference in the standard potential of their constituents, such as stainless steel (see ref. 5 for example) or alloys used for marine applications, such as CuZn or CuAl. 相似文献