首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   5262篇
  免费   283篇
  国内免费   62篇
耳鼻咽喉   35篇
儿科学   171篇
妇产科学   79篇
基础医学   681篇
口腔科学   381篇
临床医学   415篇
内科学   1284篇
皮肤病学   153篇
神经病学   298篇
特种医学   393篇
外科学   491篇
综合类   30篇
预防医学   457篇
眼科学   73篇
药学   428篇
中国医学   46篇
肿瘤学   192篇
  2023年   39篇
  2022年   65篇
  2021年   145篇
  2020年   101篇
  2019年   142篇
  2018年   144篇
  2017年   104篇
  2016年   122篇
  2015年   132篇
  2014年   150篇
  2013年   251篇
  2012年   346篇
  2011年   333篇
  2010年   204篇
  2009年   186篇
  2008年   279篇
  2007年   317篇
  2006年   255篇
  2005年   217篇
  2004年   181篇
  2003年   142篇
  2002年   124篇
  2001年   113篇
  2000年   122篇
  1999年   94篇
  1998年   88篇
  1997年   104篇
  1996年   120篇
  1995年   83篇
  1994年   74篇
  1993年   68篇
  1992年   61篇
  1991年   56篇
  1990年   67篇
  1989年   67篇
  1988年   70篇
  1987年   59篇
  1986年   65篇
  1985年   55篇
  1984年   20篇
  1983年   29篇
  1982年   20篇
  1981年   13篇
  1980年   13篇
  1979年   13篇
  1978年   17篇
  1976年   15篇
  1975年   17篇
  1969年   19篇
  1968年   11篇
排序方式: 共有5607条查询结果,搜索用时 15 毫秒
51.
In a human in-vitro fertilization (IVF) programme, the effect of co- culture of embryos with human fibroblasts was evaluated with respect to pregnancy rate and embryo development. Patients were included in the study after giving informed written consent. The IVF treatments were randomly assigned by stratification of both age (<36 versus > or =36 years) and previous IVF attempts (yes versus no). After fertilization was established, the zygotes were transferred to a 4-well dish with or without fibroblasts and cultured for 2 days. On the third day after ovum pick-up (OPU), cell number and quality [5 (good) to 1 (poor)] of the embryos were scored and a maximum of three embryos was transferred. Supernumerary embryos of good quality were cryopreserved. The design of this study was a group sequential trial with the objective of detecting differences between pregnancy rates following IVF with conventional incubation or incubation in co-culture with fibroblasts. This design included one evaluation at half-way data collection. In the study, 148 patients had an OPU, of whom 77 were allocated to the co-culture group. There was no statistically significant difference in pregnancy rate, cell number and embryo quality between the two groups. The ongoing pregnancy rate per embryo transfer was 27% in co-culture and 30% in the conventional culture group. The implantation rates per transferred embryo were 17 and 18% respectively. Using a multivariate logistic regression model for the probability of ongoing pregnancies, the odds ratio of co-culture, adjusted for age and previous IVF attempts, was not statistically significant. In conclusion, co-culture with human fibroblasts does not contribute to an improvement of embryo quality nor to a higher pregnancy rate after IVF in an unselected group of patients.   相似文献   
52.
Alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors have been identified mostly as postsynaptic receptors mediating fast glutamatergic synaptic transmission. However, neurochemical studies based on the modulation of neurotransmitter release have suggested the existence of presynaptic AMPA receptors. We have used a recently described technique that allows a high-purity fractionation of the pre- and postsynaptic proteins of synaptic junctions to evaluate the distribution of the different AMPA receptor subunits in rat hippocampal synapses. Surprisingly, we found very high levels of GluR1- and GluR2/3-like immunoreactivity in the presynaptic fraction, but also in the postsynaptic and extrasynaptic fractions. GluR4-like immunoreactivity was much less abundant but was still detected, predominantly in the postsynaptic fraction. This methodology appears to be far more sensitive than the classical immunogold electron microscopy to determine the localization of synaptic receptors.  相似文献   
53.
C V Cunha  J V Costa 《Virology》1992,187(1):73-83
Infection of Vero cells with African swine fever virus (ASFV) resulted in a marked increase in ribonucleotide reductase activity. The induction of ribonucleotide reductase was detected early after infection and was proportional to the multiplicity of infection. Inhibition of viral DNA replication did not affect the induction of the enzyme. Several characteristics could distinguish the virus-induced from the normal cell enzyme. ASFV-induced ribonucleotide reductase was inhibited by magnesium, was more strongly inhibited by hydroxyurea, and had a fourfold lower Km. The virus-induced enzyme was inhibited by deoxyribonucleoside triphosphates and by ATP. The isolation of hydroxyurea-resistant ASFV mutants provided genetic evidence for the viral origin of the induced ribonucleotide reductase. The resistance to hydroxyurea was due to a threefold overproduction of ribonucleotide reductase, as compared to enzyme induction by wild-type ASFV. Hydroxyurea had similar effect in vitro on ribonucleotide reductases induced by wild-type or mutant virus. The gene for the small subunit of the viral enzyme was mapped within a 2.3-kb fragment by hybridization with an oligonucleotide probe designed from a conserved aminoacid sequence of eukaryotic and viral ribonucleotide reductases.  相似文献   
54.
Summary The anatomic constraints imposed on a total artificial heart (TAH) require specific anatomic studies. A thoracic anatomic study was performed with a scanning device equipped with three-dimensional (3-D) reconstruction software on 15 male patients, between the ages of 41 to 63 years (52 ± 6 years). All were candidates for heart transplantation. The 3-D reconstructions of the cardiovascular structures obtained from surgical anatomy data specific to TAH implantation allowed a volumetric measurement of these structures. A modeling diagram of these structures permitted reproducible quantitative measurements of the 35 geometrical parameters which characterized shape, orientation, and position of these structures within the thorax. Most of the measured parameters were characterized by low variability (coefficient of variation from 10 to 25%).
Modélisation tridimensionnelle de l'anatomie du cur et des gros vaisseaux
Résumé Les contraintes anatomiques imposées au cur artificiel total (CAT) nécessitent des études anatomiques spécifiques. Une étude anatomique thoracique a été réalisée avec un scanner doté d'un logiciel de reconstruction tridimensionnelle (3-D) chez 15 patients, tous de sexe masculin, agés de 41 à 63 ans (52 ± 6 ans), et candidats à une transplantation cardiaque. Les reconstructions 3-D des structures cardio-vasculaires réalisées selon les données de l'anatomie chirurgicale propre à l'implantation du CAT ont permis la mesure volumétrique de ces structures. Un schéma de modélisation de ces structures a permis des mesures quantitatives reproductibles de 35 paramètres géométriques caractéristiques de la forme, de l'orientation, de la position de ces structures dans le thorax. Les résultats de ces mesures ont pu être exprimés en termes statistiques. La plupart des paramètres mesurés étaient caractérisés par une faible variabilité (coefficients de variations de 10 à 25%).
  相似文献   
55.
The persistence of Cytomegalovirus (CMV) with alteration of cell surface expression in certain tissues may initiate the tissue destruction that leads to the clinical manifestations of Sjogren's Syndrome. Salivary gland and lacrimal gland ductal cells are immunologically attacked due to CMV antigenic expression. The destruction of these ducts leads to xerostomia and keratonconjunctivitis sicca, the hallmarks of Sjogren's Syndrome.  相似文献   
56.
Summary The angular points are the ligamentous and tendinous structures that reinforce the posteromedial and posterolateral capsule of the knee and share in fixation of the posterior horns of the menisci. They are often damaged in acute injuries and this is usually associated with ruptures of the cruciate and collateral ligaments and may add to the degree of laxity. We describe the normal appearance of these structures in terms of the sectional anatomy, correlated with the lesional appearances of complete and incomplete ruptures and associated meniscal detachments as shown by clinical testing and arthrotomy findings.
IRM des points d'angle du genou : bases anatomiques et applications aux genoux traumatiques
Résumé Les points d'angle sont des structures ligamentaires et tendineuses qui renforcent la capsule postéro-médiale et postéro-latérale et participent à la fixation des cornes postérieures des ménisques. Leurs lésions, fréquentes au cours des traumatismes aigus, sont généralement associées à des ruptures des ligaments croisés et des ligaments collatéraux et peuvent être source d'une aggravation de la laxité. Nous rapportons, en corrélation avec l'anatomie en coupe, l'aspect normal de ces structures, et en corrélation avec les données de l'arthrotomie et du testing les aspects lésionnels observés au cours des traumatismes : ruptures complètes, incomplètes et désinsertions méniscales associées.
  相似文献   
57.
58.
Objective and design: We previously described the visceral antinociceptive property of α, β-amyrin in a mouse model of cystitis induced by cyclophosphamide (CPM). This study examined the contribution of vanilloid-1 (TRPV1), peripheral NK1 receptors to CPM-evoked nociceptive behaviors and bladder edema, and its possible modulation by α, β-amyrin. Methods: The effect of α, β-amyrin (10, 30, and 100 mg/kg, p. o.) and N-acetylcysteine (NAC) on CPM (400 mg/kg, i. p.)-induced cystitis was studied in mice. Sensory deafferentation was done by a high dose capsaicin. The parameters analysed were: CPM-evoked noxious behaviors, bladder edema, vascular permeability, and NK1 immunoreactivity. To assess the role of K+ ATP channels in α, β-amyrin effect, animals were pretreated with glibenclamide. Results: α, β-amyrin (30 and 100 mg/kg) and NAC significantly (p < 0.01) suppressed the visceral pain-related behaviors and NK1 immunoreactivity, but bladder edema was reduced weakly. Glibenclamide reversed the effects of α, β-amyrin. Sensory deafferentation by capsaicin significantly reduced the nociceptive responses and the NK1 immunoreactivity to noxious stimulation by CPM. Conclusions: α, β-amyrin attenuates CPM-induced visceral pain and bladder edema by mechanisms that involve, at least in part, a block either of Substance P release or its receptor function, and partly by opening K+ ATP channels. Received 13 February 2007; returned for revision 13 April 2007; accepted by G. Geisslinger 14 May 2007  相似文献   
59.
Histone H1 of most eukaryotes is phosphorylated during the cell cycle progression and seems to play a role in the regulation of chromatin structure, affecting replication and chromosome condensation. In trypanosomatids, histone H1 lacks the globular domain and is shorter when compared with the histone of other eukaryotes. We have previously shown that in Trypanosoma cruzi, the agent of Chagas' disease, histone H1 is phosphorylated and this increases its dissociation from chromatin. Here, we demonstrate using mass spectrometry analysis that T. cruzi histone H1 is only phosphorylated at the serine 12 in the sequence SPKK, a typical cyclin-dependent kinase site. We also found a correlation between the phosphorylation state of histone H1 and the cell cycle. Hydroxyurea and lactacystin, which, respectively, arrest parasites at the G1/S and G2/M stages of the cell cycle, increased the level of histone H1 phosphorylation. Cyclin-dependent kinase-related enzymes TzCRK3, and less intensely the TzCRK1 were able to phosphorylate histone H1 in vitro. Histone H1 dephosphorylation was prevented by treating the parasites with okadaic acid but not with calyculin A. These findings suggest that T. cruzi histone H1 phosphorylation is promoted by cyclin dependent kinases, present during S through G2 phase of the cell cycle, and its dephosphorylation is promoted by specific phosphatases.  相似文献   
60.
Some medical applications rely on the use of colour in the diagnostic process, even when poor colour reproduction can affect diagnosis. In this paper, we investigate the effect colour distortion can have on assessment of livers for possible transplantation. We compare the diagnostic effects for the likely colour shifts when illuminant and camera remain uncalibrated or when a monitor is incorrectly calibrated. We describe methods that can result in accurate reproduction of image colour on visual displays and determine whether accurate colour reproduction is necessary for effective liver assessment.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号