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   1500篇
  免费   117篇
  国内免费   8篇
耳鼻咽喉   7篇
儿科学   83篇
妇产科学   8篇
基础医学   185篇
口腔科学   36篇
临床医学   113篇
内科学   203篇
皮肤病学   24篇
神经病学   128篇
特种医学   358篇
外科学   134篇
综合类   47篇
预防医学   45篇
眼科学   32篇
药学   156篇
中国医学   1篇
肿瘤学   65篇
  2021年   8篇
  2020年   11篇
  2019年   11篇
  2018年   27篇
  2017年   8篇
  2016年   46篇
  2015年   42篇
  2014年   48篇
  2013年   62篇
  2012年   56篇
  2011年   48篇
  2010年   70篇
  2009年   76篇
  2008年   56篇
  2007年   49篇
  2006年   58篇
  2005年   69篇
  2004年   52篇
  2003年   64篇
  2002年   53篇
  2001年   37篇
  2000年   48篇
  1999年   28篇
  1998年   50篇
  1997年   53篇
  1996年   50篇
  1995年   38篇
  1994年   32篇
  1993年   34篇
  1992年   17篇
  1991年   20篇
  1990年   23篇
  1989年   35篇
  1988年   28篇
  1987年   20篇
  1986年   23篇
  1985年   21篇
  1984年   14篇
  1983年   16篇
  1982年   10篇
  1981年   18篇
  1980年   9篇
  1979年   6篇
  1978年   6篇
  1977年   13篇
  1976年   12篇
  1971年   6篇
  1970年   4篇
  1969年   6篇
  1966年   6篇
排序方式: 共有1625条查询结果,搜索用时 843 毫秒
1.
A practice audit of oral contraceptive users   总被引:1,自引:0,他引:1  
  相似文献   
2.
The development of intrinsic, N-methyl-D-aspartate (NMDA) receptor-mediated voltage oscillations and their dependence on co-activation of 5-hydroxytryptamine (5HT) receptors was explored in motor neurons of late embryonic and early larval Xenopus laevis. Under tetrodotoxin, 100 μM NMDA elicited a membrane depolarization of around 20 mV, but did not lead to voltage oscillations. However, following the addition of 2–5 μM 5HT, oscillations were observed in 12% of embryonic and 70% of larval motor neurons. The voltage oscillations depended upon co-activation of NMDA and 5HT receptors since they were curtailed by selectively blocking NMDA receptors with D-2-amino-5-phosphonovaleric acid (APV) or by excluding Mg2+ from the experimental saline. 5HT applied in the absence of NMDA also failed to elicit oscillations. Oscillations could be induced by the non-selective 5HT1a receptor agonist, 5-carboxamidotryptamine (5CT) and both 5HT- and 5CT-induced oscillations were abolished by pindobind-5HT1, a selective 5HT1a receptor antagonist. To test whether 5HT enables voltage oscillations by modulating the voltage-dependent block of NMDA channels by Mg2+, membrane conductance was monitored under tetrodotoxin. Although 5HT caused membrane hyperpolarization of 4–8 mV, there was little detectable change in conductance. NMDA application caused an approximate 20 mV depolarization and an ‘apparent’ decrease in conductance, presumably due to the conductance pulse bringing the membrane into a voltage region where Mg2+ blocks the NMDA ionophore. 5HT further decreased conductance, which we propose is due to its enhancement of the voltage-dependent Mg2+ block. When the membrane potential was depolarized by ~20 mV via depolarizing current injection (to mimic the NMDA-induced depolarization), 5HT increased rather than decreased membrane conductance. Furthermore, 5HT did not affect the increase in membrane conductance following NMDA applications in zero Mg2+ saline. The results suggest that intrinsic, NMDA receptor-mediated voltage oscillations develop in a brief period after hatching, and that they depend upon the co-activation of 5HT and NMDA receptors. The enabling function of 5HT may involve the facilitation of the voltage-dependent block of the NMDA ionophore by Mg2+ through activation of receptors with 5HT1a-like pharmacology.  相似文献   
3.
4.
5.
The aim of the study was to determine whether a prior diagnostic testicle biopsy can predict success or failure of testicular sperm extraction (TESE) with intracytoplasmic sperm injection (ICSI) in patients with non-obstructive azoospermia caused by testicular failure, and what is the minimum threshold of sperm production in the testis which must be surpassed for spermatozoa to reach the ejaculate. Forty- five patients with non-obstructive azoospermia caused by testicular failure underwent diagnostic testicle biopsy prior to a planned future TESE-ICSI procedure. The diagnostic testicle biopsy was analysed quantitatively, and correlated with the quantitative findings of spermatogenesis in patients with normal spermatogenesis, as well as with the results of subsequent attempts at TESE-ICSI. Men with non- obstructive azoospermia caused by germinal failure had a mean of 0-6 mature spermatids/seminiferous tubule seen on a diagnostic testicle biopsy, compared to 17-35 mature spermatids/tubule in men with normal spermatogenesis and obstructive azoospermia. These findings were the same for all types of testicular failure whether Sertoli cell only, maturation arrest, cryptorchidism, or post-chemotherapy azoospermia. Twenty-two of 26 men with mature spermatids found in the prior testis biopsy had successful retrieval of spermatozoa for ICSI, 12 of their partners became pregnant, and are either ongoing or delivered. The study suggests that 4-6 mature spermatids/tubule must be present in the testis biopsy for any spermatozoa to reach the ejaculate. More than half of azoospermic patients with germinal failure have minute foci of spermatogenesis which are insufficient to produce spermatozoa in the ejaculate. Prior diagnostic testicle biopsy analysed quantitatively (for the presence of mature spermatids) can predict subsequent success or failure with TESE-ICSI. Incomplete testicular failure may involve a sparse multi-focal distribution of spermatogenesis throughout the entire testicle, rather than a regional distribution. Therefore, it is possible that massive testicular sampling from many different regions of the testes may not be necessary for successful TESE-ICSI.   相似文献   
6.
β-Lactoglobulin was isolated from infant formulae that were ultra high temperature (UHT) -treated, sterilized or spray-dried. The effect of the isolated β-lactoglobulin on SfaII-fimbriae-mediated adhesion of Escherichia coli to human ileostomy glycoproteins was studied in vitro. β-Lactoglobulin isolated from sterilized formulae was found to perform significantly less well than preparations from spray-dried formulae (p = 0:05). Great heterogeneity was observed in the adhesion inhibitory capacity of β-lactoglobulin isolated from UHT-treated formulae. Therefore, no significant difference was observed between UHT-treated and sterilized formulae or spray-dried formulae (p < 0:10). It can be hypothesized that β-lactoglobulin from spray-dried and some UHT-treated infant formulae may affect the colonization of mucous membranes by E. coli strains causing neonatal septicaemia and meningitis.  相似文献   
7.
Zusammenfassung Die Pankreaskopfresektion in der Modifikation nach Traverso-Longmire, mit Erhaltung eines funktionierenden Pylorus, hat gegenüber der Kausch-Whipple-Operation die Vorteile, daß Anastomosenulzera vermieden werden und daß die Patienten postoperativ eine bessere und schnellere Gewichtszunahme haben. Indikationen waren bisher die Papillenkarzinome und periampulare Tumoren. Bei den Adenokarzinomen lassen sich mit der Pyloruserhaltung gleich gute Überlebensraten erzielen. Unsere Ergebnisse von 56 Pyloruserhaltungen, davon 32 beim duktalen Karzinom und 28 Kausch-Whipple-Operationen in den Jahren von 1985–1993, belegen gleiche Überlebensraten, wie dies bereits für das Papillenkarzinom gezeigt werden konnte. Die Überlebenskurven zeigen, daß die Radikalität nicht von der Magenteilentfernung, sondern von der Resektion an den posterioren und retroperitonealen Resektionsrändern abhängt.
Current indications for pylorus preservation in duodenopancreatic head resection in malignancies
The Whipple procedure has been improved by preservation of a functioning pylorus. A functioning pylorus is important because marginal ulceration is avoided and, compared to the standard Whipple procedure with gastric resection, more patients can gain weight postoperatively. The most common indications are carcinomas of ampulla of Vater and periampullary tumors. In patients with pancreatic adenocarcinoma the pylorus-preserving variety results in equal or better survival rates. In 56 patients with pylorus preservation, 32 with ductal carcinoma, and 28 with Kausch-Whipple between 1985 and 1993, our results showed slightly better survival rates and better post-operative nutrition. The weakest aspect of the radical resection addresses the retroperitoneal margin of the pancreas head and not the gastric resection.
  相似文献   
8.
The dominant cone-rod dystrophy gene CORD6 has previously been mapped to within an 8 cM interval on chromosome 17p12-p13. The retinal- specific guanylate cyclase gene (RETGC-1), which maps to within this genetic interval and previously was implicated in Leber's congenital amaurosis, was screened for mutations within this family and in a panel of small families and individuals with various cone and cone- rod dystrophy phenotypes. A missense mutation (E837D) was identified in affected members of the CORD6 family, as well as a second missense mutation (R838C) in three other families with dominant cone-rod dystrophy. RETGC-1 is only the fourth gene to be implicated in cone-rod dystrophy and this is the first report of dominant mutations in this gene.   相似文献   
9.
In human in-vitro fertilization (IVF), the oocytes are surrounded by cumulus and corona cells at the time of insemination so that their maturity cannot easily be evaluated. The best IVF results are obtained if the oocytes are inseminated 2-6 h after retrieval. In the intracytoplasmic sperm injection (ICSI) procedure, the oocytes are denuded by enzymatic and mechanical treatment in order to be able to perform the injection. As a consequence, the nuclear maturity of the oocytes can be evaluated and only those that have extruded the first polar body are injected. However, metaphase-II oocytes that have not yet reached cytoplasmic maturity cannot be recognized. The purpose of this study was to investigate the effect of different timing of cumulus- corona cell removal and injection on the outcome of ICSI. For this we allowed the oocytes to complete in-vitro cytoplasmic maturation in two different culture conditions: (i) surrounded by their cumulus and corona cells or (ii) totally denuded. We performed three different studies on sibling oocytes obtained after a standardized buserelin/human menopausal gonadotrophin (HMG) protocol. We investigated the effect of early (1-2 h after retrieval) and late (5-6 h after retrieval) oocyte denudation and injection on the survival and fertilization of the injected oocytes and on embryo cleavage after fertilization. We found no statistically significant differences between early and late injection, indicating that after a standardized buserelin/HMG protocol the metaphase-II oocytes do not need time for further cytoplasmic maturation. Furthermore, a different timing of cumulus-corona cell removal has no effect on the outcome of ICSI, suggesting that the surrounding cells are not necessary for survival, fertilization and cleavage after ICSI.   相似文献   
10.
Serum follicle stimulating hormone (FSH) is routinely measured when evaluating the infertile male for intracytoplasmic sperm injection (ICSI). However, among the sperm parameters, only its relationship with sperm concentration is well documented. Few investigations concern the relationship between FSH and sperm motility and morphology, and the results of ICSI. A retrospective study of 316 couples who underwent ICSI was carried out to determine the relationships between serum FSH concentrations in the male and (i) standard sperm parameters_(concentration, motility and morphology) and (ii) fertilization, cleavage, pregnancy and implantation rates after ICSI. There was an inverse correlation with sperm concentration and total motility but no relationship was found with progressive motility and sperm morphology. Neither was any relationship found between serum FSH and fertilization, cleavage, pregnancy and implantation rates, and the results of ICSI. These findings suggest the need to review the routine measurement of serum FSH in the infertile male when ICSI is the planned treatment procedure.   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