全文获取类型
收费全文 | 15490篇 |
免费 | 1201篇 |
国内免费 | 54篇 |
专业分类
耳鼻咽喉 | 209篇 |
儿科学 | 330篇 |
妇产科学 | 216篇 |
基础医学 | 1912篇 |
口腔科学 | 433篇 |
临床医学 | 1536篇 |
内科学 | 3599篇 |
皮肤病学 | 187篇 |
神经病学 | 1219篇 |
特种医学 | 644篇 |
外科学 | 2303篇 |
综合类 | 317篇 |
一般理论 | 16篇 |
预防医学 | 1161篇 |
眼科学 | 592篇 |
药学 | 1051篇 |
中国医学 | 38篇 |
肿瘤学 | 982篇 |
出版年
2022年 | 82篇 |
2021年 | 192篇 |
2020年 | 97篇 |
2019年 | 191篇 |
2018年 | 214篇 |
2017年 | 172篇 |
2016年 | 207篇 |
2015年 | 250篇 |
2014年 | 401篇 |
2013年 | 667篇 |
2012年 | 829篇 |
2011年 | 905篇 |
2010年 | 494篇 |
2009年 | 477篇 |
2008年 | 882篇 |
2007年 | 1016篇 |
2006年 | 1032篇 |
2005年 | 991篇 |
2004年 | 1057篇 |
2003年 | 976篇 |
2002年 | 975篇 |
2001年 | 138篇 |
2000年 | 97篇 |
1999年 | 171篇 |
1998年 | 231篇 |
1997年 | 208篇 |
1996年 | 183篇 |
1995年 | 192篇 |
1994年 | 145篇 |
1993年 | 150篇 |
1992年 | 88篇 |
1991年 | 94篇 |
1990年 | 100篇 |
1989年 | 97篇 |
1988年 | 100篇 |
1987年 | 81篇 |
1986年 | 87篇 |
1985年 | 110篇 |
1984年 | 170篇 |
1983年 | 148篇 |
1982年 | 218篇 |
1981年 | 219篇 |
1980年 | 170篇 |
1979年 | 94篇 |
1978年 | 119篇 |
1977年 | 145篇 |
1976年 | 140篇 |
1975年 | 126篇 |
1974年 | 98篇 |
1973年 | 90篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Single-Step Multiplex PCR Assay for Characterization of New World Leishmania Complexes 总被引:2,自引:0,他引:2
下载免费PDF全文
![点击此处可从《Journal of clinical microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Eva Harris Gerald Kropp Alejandro Belli Betzab Rodriguez Nina Agabian 《Journal of clinical microbiology》1998,36(7):1989-1995
We have developed a PCR assay for one-step differentiation of the three complexes of New World Leishmania (Leishmania braziliensis, Leishmania mexicana, and Leishmania donovani). This multiplex assay is targeted to the spliced leader RNA (mini-exon) gene repeats of these organisms and can detect all three complexes simultaneously, generating differently sized products for each complex. The assay is specific to the Leishmania genus and does not recognize related kinetoplastid protozoa, such as Trypanosoma cruzi, Trypanosoma brucei, and Crithidia fasciculata. It correctly identified Leishmania species with a broad geographic distribution in Central and South America. The sensitivity of the PCR amplification ranged from 1 fg to 10 pg of DNA (0.01 to 100 parasites), depending on the complex detected. Crude extracts of cultured parasites, prepared simply by boiling diluted cultures, served as excellent templates for amplification. Crude preparations of clinical material were also tested. The assay detected L. braziliensis in dermal scrapings from cutaneous leishmanial lesions, Leishmania chagasi in dermal scrapings of atypical cutaneous leishmaniasis, and L. mexicana from lesion aspirates from infected hamsters. We have minimized the material requirements and maximized the simplicity, rapidity, and informative content of this assay to render it suitable for use in laboratories in countries where leishmaniasis is endemic. This assay should be useful for rapid in-country identification of Leishmania parasites, particularly where different Leishmania complexes are found in the same geographical area. 相似文献
82.
The dynamic behavior of a batch culture of yeast with a rate-limiting nutrient was analyzed by examining the cell number density, cell size distribution, and concentration of a rate-limiting nutrient. The particular strain of S. cerevisiae studied grows only when the medium contains L-tryptophan. The cell number, volume distribution, and external L-tryptophan concentration were measured at successive times in the development of the culture. A mathematical model was developed to simulate the experimental data and provide a framework for understanding the dynamics of the cell growth and division in terms of cellular events. A nonlinear optimization procedure was specially adapted to estimate model parameters. 相似文献
83.
Gerald L. Stoner 《Brain pathology (Zurich, Switzerland)》1993,3(3):213-227
Multiple sclerosis (MS) is generally considered to be an autoimmune disorder with myelin as the target and with several unidentified viruses playing ancillary roles, possibly through molecular mimicry. Although this paradigm has led to important progress on potential mechanisms of myelin loss, neither a target antigen in myelin nor a triggering mechanism has yet been identified, leaving the etiology of MS still unknown. Animal models of viral demyelination and studies showing that JC virus (JCV), the polyomavirus which causes progressive multifocal leukoencephalopathy (PML), may be latent in some normal human brains suggest another possibility. A host immune response targeting proteins expressed at low levels from viral DNA latent in the central nervous system (CNS) might underlie a focal demyelinating disease such as MS. A shift from autoimmunity to a latent-virus model is not a trivial substitution of target antigens. This shift would expand the search for a definitive laboratory test for MS and could lead to improved therapeutic and preventive approaches. 相似文献
84.
85.
The effect of direct intrahypothalamic nitric oxide (NO) administration on the release of selected amino acids in the hypothalamic supraoptic nucleus (SON) with and without concomitant forced swimming was investigated. Adult male Wistar rats were chronically fitted with U-shaped microdialysis probes in the SON and forced to swim for 10-min in 20-degree C warm water. Thirty-min microdialysis samples were collected before, during and after the forced swimming period while NO was administered into the SON via microdialysis. The results show that NO administration in combination with forced swimming affects the release of aspartate, glutamate, taurine, and gamma aminobutyric acid (GABA) in different patterns. Whereas the release of the excitatory amino acids aspartate and glutamate was triggered only during NO administration and forced swimming, the inhibitory amino acids GABA and taurine were found in the extracellular fluid in increased concentrations also after the treatment. These data indicate that NO administration differently affects the release of excitatory and inhibitory amino acids within the SON. Thus, SON neurons which contain high concentrations of neuronal NO synthase, might contribute to the regulation of their own secretory activity by releasing NO that controls the orchestrated release of excitatory and inhibitory amino acids from axon terminals of afferences and interneurons as well as release from glial cells. 相似文献
86.
Recent experiments have shown that shortening and stretching of sarcomeres in single activated and unactivated myofibrils occur in stepwise fashion (Yang et al. (1998) Biophys J 74: 1473-1483; Blyakhman et al. (2001) Biophys J 81: 1093-1100; Yakovenko et al. (2002) Am J Physiol Cell Physiol 283: 735-742). Here, we carried out measurements on single myofibrils from rabbit psoas muscle to investigate steps in unactivated specimens in more detail. Activated and unactivated myofibrils were released and stretched in ramp-like fashion. The time course of length change in the single sarcomere was consistently stepwise. We found that in the unactivated myofibrils, step size depended on initial sarcomere length, diminishing progressively with increase of initial sarcomere length, whereas in the case of activated sarcomeres, step size was consistently 2.7 nm. 相似文献
87.
Wheat streak mosaic virus is a Tritimovirus, a member of the Potyviridae family, which includes the very large Potyvirus genus. We have examined wheat streak mosaic virus by electron microscopy and fiber diffraction from partially oriented sols, and analyzed the results to estimate the symmetry and structural parameters of the viral helix. The virions have an apparent radius of 63 +/- 5 A. The viral helix has a pitch of 33.4 A +/- 0.6 A. There appear to be 6.9 subunits per turn of the helix, although we cannot completely eliminate values of 5.9 or 7.9 for this parameter. 相似文献
88.
89.
Richard Meehan Ulric Duncan Laureen Neale Gerald Taylor Harold Muchmore Nan Scott Keith Ramsey Eric Smith Paul Rock Randall Goldblum Charles Houston 《Journal of clinical immunology》1988,8(5):397-406
We investigated the effects on immune function after progressive hypobaric hypoxia simulating an ascent to 25,000 ft (7620 m) over 4 weeks. Multiple simultaneousin vitro andin vivo immunologic variables were obtained from subjects at sea level, 7500 ft (2286 m), and 25,000 ft during a decompression chamber exposure. Phytohemag-glutinin-stimulated thymidine uptake and protein synthesis in mononuclear cells were reduced at extreme altitudes. Mononuclear-cell subset analysis by flow cytometry disclosed an increase in monocytes without changes in B cells or T-cell subsets. Plasma IgM and IgA but not IgG levels were increased at altitudes, whereas pokeweed mitogen-stimulatedin vitro IgG, IgA, and IgM secretion was unchanged. During exposure to 25,000 ft,in vitro phytohemagglutinin-stimulated interferon production and natural killer-cell cytotoxicity did not change statistically, but larger intersubject differences occurred. IgA and lysozyme levels (nasal wash) and serum antibodies to nuclear antigens were not influenced by altitude exposure. These results suggest that T-cell activation is blunted during exposure to severe hypoxemia, whereas B-cell function and mucosal immunity are not. Although the mechanism of alteredin vitro immune responsiveness after exposure to various environmental stressors has not been elucidated in humans, hypoxia may induce alterations in immune regulation as suggested byin vitro immune assays of effector-cell function.Some of this study's results were presented as an abstract at the FASEB meeting in St. Louis, Missouri, 1986. 相似文献
90.
Summary of complementation groups of UV-sensitive CHO cell mutants isolated by large-scale screening 总被引:7,自引:0,他引:7
Busch David; Greiner Carol; Lewis Kathy; Ford Ruth; Adair Gerald; Thompson Larry 《Mutagenesis》1989,4(5):349-354
A summary is given for the lineage and complementation groupassignments of 153 UV-sensitive mutants of the CHO AA8 cellline. The distribution of mutants among six complementationgroups was highly non-random, with the great majority of theisolates belonging to groups 1 and 2. This asymmetry is consistentwith the known hemizygosity of these two linked loci in CHOcells. The relative numbers of mutants induced in group 2 wasfound to depend greatly on the type of mutagen used. Mutagenesiswith UV radiation, ethyl methanesulfonate (EMS), N-methyl-N'-nitro-N-nitroso-guanidine and 7-bromomethylbenz[a]anthraceneproduced high frequencies of group 2 mutants. In contrast, ICR170and ICR191, which are thought to produce mostly frameshift mutations,yielded very few mutants in group 2. These results are of particularimportance in light of the recent finding that the human ERCC2gene, which corrects group 2 mutants, has very strong homologywith the yeast gene RAD3. RAD3 is an essential gene for viabilityin yeast, and the low recovery of group 2 mutants using theframeshift agents strongly suggests that frameshift mutationstend to be lethal in the hamster ERCC2 locus. Several mutagen-sensitivedouble mutants were isolated in two-step selections from EMS-,mitomycin C- or UV-sensitive parental cells, including the lineUVU1, the first mammalian line with two mutations that affectUV sensitivity. The first mutation inactivated excision repair,and the second mutation appears to have affected some otherrecovery process. UVU1 should be useful for studying recoveryprocesses that are separate from nucleotide excision repair.
1To whom correspondence should be addressed 相似文献