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   11007篇
  免费   1126篇
  国内免费   13篇
耳鼻咽喉   133篇
儿科学   441篇
妇产科学   291篇
基础医学   1624篇
口腔科学   221篇
临床医学   1100篇
内科学   1924篇
皮肤病学   124篇
神经病学   1245篇
特种医学   526篇
外科学   1385篇
综合类   321篇
一般理论   29篇
预防医学   1021篇
眼科学   222篇
药学   839篇
中国医学   4篇
肿瘤学   696篇
  2021年   95篇
  2020年   93篇
  2019年   125篇
  2018年   140篇
  2017年   143篇
  2016年   122篇
  2015年   148篇
  2014年   219篇
  2013年   329篇
  2012年   408篇
  2011年   409篇
  2010年   251篇
  2009年   219篇
  2008年   412篇
  2007年   435篇
  2006年   436篇
  2005年   416篇
  2004年   436篇
  2003年   406篇
  2002年   442篇
  2001年   395篇
  2000年   391篇
  1999年   342篇
  1998年   145篇
  1997年   128篇
  1996年   162篇
  1995年   117篇
  1994年   117篇
  1993年   138篇
  1992年   296篇
  1991年   304篇
  1990年   288篇
  1989年   292篇
  1988年   249篇
  1987年   271篇
  1986年   244篇
  1985年   225篇
  1984年   186篇
  1983年   203篇
  1982年   119篇
  1981年   103篇
  1980年   88篇
  1979年   180篇
  1978年   125篇
  1977年   96篇
  1976年   106篇
  1974年   92篇
  1973年   85篇
  1972年   95篇
  1971年   86篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
We examined the internal jugular veins in three groups of patients who had undergone (1) a functional neck dissection and radiotherapy, (2) a functional neck dissection alone, or (3) radiotherapy alone, using a noninvasive color Doppler ultrasound scan. The internal jugular veins were ultrasonically bilaterally normal in 18% of patients who had undergone a functional neck dissection and radiotherapy, in 88% of patients who had undergone a functional neck dissection alone, and in 57% of patients who had undergone radiotherapy alone. The combination of a functional neck dissection and radiotherapy significantly affected the internal jugular vein when compared with a functional neck dissection alone.  相似文献   
72.
73.
A case of a 4-year-old boy with trisomy of the long arm of chromosome 9 is described (46,XY, der (9), t (9;9) (q32;q12)). The trisomy is probably the result of a translocation of the long arm of the chromosome from one homologue to the other in a parental gonad. The clinical features of the child which include severe developmental retardation, bird-like facies, tapered fingers, and flexion contractures of the legs are similar to those of the few cases described of trisomy of the whole chromosome.  相似文献   
74.
To assess DNA immunization as a strategy for protecting against HIV infection in humans, we utilized SIVmne infection of Macaca fascicularis as a vaccine challenge model with moderate pathogenic potential. We compared the efficacy of DNA immunization alone and in combination with subunit protein boosts. All of the structural and regulatory genes of SIVmne clone 8 were cloned into mammalian expression vectors under the control of the CMV IE-1 promoter. Eight M. fascicularis were immunized twice with 3 mg of plasmid DNA divided between two sites; intramuscular and intradermal. Four primed macaques received a further two DNA immunizations at weeks 16-36, while the second group of four were boosted with 250 microg recombinant gp160 plus 250 microg recombinant Gag-Pol particles formulated in MF-59 adjuvant. Half of the controls received four immunizations of vector DNA; half received two vector DNA and two adjuvant immunizations. As expected, humoral immune responses were stronger in the macaques receiving subunit boosts, but responses were sustained in both groups. Significant neutralizing antibody titers to SIVmne were detected in one of the subunit-boosted animals and in none of the DNA-only animals prior to challenge. T-cell proliferative responses to gp160 and to Gag were detected in all immunized animals after three immunizations, and these responses increased after four immunizations. Cytokine profiles in PHA-stimulated PBMC taken on the day of challenge showed trends toward Thl responses in 2/4 macaques in the DNA vaccinated group and in 1/4 of the DNA plus subunit vaccinated macaques; Th2 responses in 3/4 DNA plus subunit-immunized macaques; and Th0 responses in 4/4 controls. In bulk CTL culture, SIV specific lysis was low or undetectable, even after four immunizations. However, stable SIV Gag-Pol- and env-specific T-cell clones (CD3+ CD8+) were isolated after only two DNA immunizations, and Gag-Pol- and Nef-specific CTL lines were isolated on the day of challenge. All animals were challenged at week 38 with SIVmne uncloned stock by the intrarectal route. Based on antibody anamnestic responses (western, ELISA, and neutralizing antibodies) and virus detection methods (co-culture of PBMC and LNMC, nested set PCR- of DNA from PBMC and LNMC, and plasma QC-PCR), there were major differences between the groups in the challenge outcome. Surprisingly, sustained low virus loads were observed only in the DNA group, suggesting that four immunizations with DNA only elicited more effective immune responses than two DNA primes combined with two protein boosts. Multigenic DNA vaccines such as these, bearing all structural and regulatory genes, show significant promise and may be a safe alternative to live-attenuated vaccines.  相似文献   
75.
The reactivities of antibodies with branched and monomeric peptides were compared in ELISA assays. We found that lower amounts of antibodies could be detected with branched peptides than with monomeric peptides. This was observed with a monoclonal antibody and with antibodies in the sera of various HIV-positive individuals. To investigate the physical aspects of branched peptides important for the observed increase in sensitivity, glycine spacers of different lengths were introduced between the branched lysine core and the epitope reacting with the monoclonal antibody. The effect of the number of glycine residues, both on the sensitivity of antibody detection and on the amount of branched peptide needed to produce a given signal, was studied and the optimum was found at 4-5 residues. We discuss the basis for these findings and conclude that the routine use of branched peptides for serodiagnosis will give both greater sensitivity and appreciable cost savings.  相似文献   
76.
The specific binding of epidermal growth factor (EGF), platelet-derived growth factor (PDGF) and insulin were measured in matching cultures of human leiomyoma and myometrial cells, along with the effects of these proteins on DNA and protein syntheses. Scatchard analyses of the binding data revealed that the EGF receptor sites/cell were significantly lower in leiomyoma than myometrial cultures. Two types of PDGF binding were observed when porcine PDGF was used, and one type was seen with human PDGF. By contrast to EGF, more PDGF receptor sites/cell were found in leiomyoma than myometrium but the receptor affinity was higher in the latter. Insulin binding was similar among the myometrial and leiomyoma cells. Protein synthesis was stimulated 3-fold by EGF, PDGF, or insulin in both cell types. DNA synthesis, was higher in myometrial than leiomyoma cells in the basal state and was stimulated by EGF, insulin, or PDGF. A synergistic stimulation (p less than 0.02) of DNA synthesis was observed in both myometrial and leiomyoma cells when EGF was added with insulin. The addition of PDGF with insulin caused only additive stimulation of DNA synthesis. However, the addition of EGF with PDGF caused a synergistic decrease (p less than 0.05) in DNA synthesis by myometrial but no leiomyoma cells. Cultures of human vascular smooth muscle cells obtained from umbilical veins gave results similar to those from myometrium. These findings single out the EGF receptor and EGF, or perhaps an EGF-like growth factor, and to a lesser degree PDGF, as potential regulators of uterine leiomyomata.  相似文献   
77.
Summary Microangiographic and histological studies, including serial sectioning, were carried out on the lungs of seven autopsy cases of transposition of the great arteries associated with interventricular septum defect. In five of the cases other cardiovascular abnormalities were also present — valvular pulmonary stenosis, pulmonary and systemic venous anomalies, atrial septal defect and coarctation of the aorta. The ages of the subjects varied from four days to 11 months. Tortuosity of the intralobular pulmonary arteries was observed in three subjects. The number, size and course of the pulmobronchial arteries were normal. A few arterial bronchopulmonary anastomoses (diameter range 50–350 µ) were demonstrated in two subjects. The diameter range of the main bronchial arteries in the aorta-injected specimens was within normal limits. The number of bronchopulmonary arteries was moderately increased in two of the older subjects. The systemic-artery supply of the pulmonary parenchyma, however, was not as prominent as in infants of the same age with isolated transposition of the great arteries.
Das intrapulmonale, arterielle Gefäßmuster bei Kindern mit Transposition der großen Arterien und Ventrikelseptumdefekt
Zusammenfassung Bei 7 Obduktionsfällen mit Transposition der großen Arterien und Ventrikelseptumdefekt wurden mikroangiographische und histologische Untersuchungen (einschl. Serienschnittstudien) der Lunge durchgeführt. Bei 5 Fällen lagen auch andere kardiovaskuläre Mißbildungen vor: Pulmonalklappenstenose, Venenanomalien, Vorhofseptumdefekte und Coarctatio aortae. Das Alter der Fälle betrug 4 Tage bis 11 Monate. Abnorm gewundene intralobuläre Pulmonalarterienäste wurden bei 3 Fällen beobachtet. Pulmobronchialarterien kamen in normaler Anzahl vor und zeigten keine Abweichungen hinsichtlich Größe oder Verlauf. Eine geringere Anzahl arterieller, bronchopulmonaler Anastomosen (Lumen 50–350 µ) wurde bei 2 der untersuchten Fälle beobachtet. Das Lumen der Hauptäste der Bronchialarterien war normal. Bei 2 der älteren Fälle war die Zahl der Bronchopulmonalarterien mäßig erhöht. Die Bronchialarterien des Lungenparenchyms zeigten jedoch keine so starke Vergrößerung und reiche Verästelung wie bei gleichaltrigen Fällen mit isolierter Transposition der großen Arterien.


This investigation has been supported by grants from the Swedish National Association against Heart and Chest Diseases, Karolinska Institutes Reservationsanslag, Carin Tryggers fond, and Stiftelsen Therese och Johan Anderssons Minne.  相似文献   
78.
CD95 (APO-1/Fas) is a member of the superfamily that includes the nerve growth factor and tumor necrosis factor receptors, OX40, CD27, CD30, and CD40. Present on a minority of resting blood lymphocytes, CD95 expression is upregulated on activated T and B lymphocytes and natural killer cells, where binding of the antigen by anti-Fas and anti-APO-1 antibodies has been shown to induce apoptosis. This CD95-mediated apoptosis is at least partially inhibited by expression of the Bcl-2 protooncogene. To evaluate possible roles of CD95 and Bcl-2 in growth regulation of lymphoid neoplasms, we studied by immunohistochemistry the expression of CD95 and Bcl-2 in 67 B- and 5 T-cell lymphomas, and 10 cases of Hodgkin's disease. In all, 29 B and 2 T cell lymphomas, and 9 cases of Hodgkin's disease expressed CD95. Compared with diffuse large B-cell and Burkitt-like lymphomas, lowgrade B-cell lymphomas more frequently expressed CD95 (52% versus 26%; P < .005). None of the B-cell small lymphocytic lymphomas or mantle cell lymphomas expressed CD95, whereas the majority of follicle center lymphomas, extranodal marginal zone B-cell lymphomas, and immunocytomas were CD95+. Of the 29 CD95+ B-cell lymphomas, only 33% of the high-grade group coexpressed Bcl-2, compared with 87% of the low-grade group (P < .04). Two of three peripheral T-cell lymphomas--including one anaplastic large cell lymphoma--expressed CD95. Staining for CD95 was seen in 9 of 10 cases of Hodgkin's disease. The infrequent expression of CD95 in high-grade B-cell lymphomas suggests an association between loss of CD95 expression/function and a more aggressive tumor grade. Whereas frequent coexpression of Bcl-2 with CD95 may protect low-grade B-cell lymphomas against CD95-mediated apoptosis, in the high-grade group such coexpression is infrequent, and other regulators besides Bcl-2 may be involved in modulating the apoptosis signal delivered by CD95.  相似文献   
79.
During the period of rapid elongation prior to the initiation of placental attachment (days 12–16 of gestation), the ovine blastocyst consists of a single layer (primarily) of roughly cuboidal trophoblastic cells with an inner lining of flattened endodermal cells. Well-developed spot desmosomes link the adjacent cell borders in both the trophoblastic and endodermal layers. The trophoblastic cells contain acid phosphatase-positive, lysosomelike organelles, the mean diameter of which increases greatly between days 12 and 16 and whose contents vary during development. Also during the developmental period studied, trophoblast cells accumulate lipid; and periodic acid-Schiff-positive binucleate cells appear within the trophoblast layer. A consistent observation throughout the 5 days of rapid growth and differentiation of the blastocyst was the death and disintegration of some trophoblast cells. These disintegrating cells are usually singly dispersed within the trophoblast, although occasionally groups of four or five are observed. The cell death may indicate overall remodelling of the blastocyst, or the cells may represent genetically deficient cells which are unable to respond to the appropriate signal to differentiate.  相似文献   
80.
The prevalence of human T-cell lymphotropic virus type 1 (HTLV-1) and HTLV-2 infection in 1992 and 1993 was determined by testing 2,152 specimens from injection drug users living in 11 geographic areas in Spain. Results obtained by an authentic HTLV-1 and -2 test were compared with those obtained by an HTLV-1 assay. HTLV infection was identified in 7 of 11 regions, with an overall prevalence of 2.5% (range, 0.4 to 11.5%). Fourty-four (81%) of 54 subjects were infected with HTLV-2; the viral strains in the remaining 10 subjects could not be serologically typed. Underestimation of HTLV infection because of the low sensitivities of HTLV-1 enzyme immunoassays for HTLV-2 antibody was relatively low (< 20%). Therefore, previous epidemiologic findings generated with HTLV-1 enzyme immunoassays appear to be reasonably accurate. Our results suggest that the rate of HTLV infection may have been increasing recently among Spanish drug users.  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