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   8264篇
  免费   505篇
  国内免费   162篇
耳鼻咽喉   14篇
儿科学   52篇
妇产科学   1657篇
基础医学   1520篇
口腔科学   19篇
临床医学   512篇
内科学   214篇
皮肤病学   139篇
神经病学   33篇
特种医学   72篇
外国民族医学   1篇
外科学   1763篇
综合类   1348篇
现状与发展   1篇
一般理论   6篇
预防医学   531篇
眼科学   22篇
药学   351篇
  3篇
中国医学   563篇
肿瘤学   110篇
  2024年   15篇
  2023年   73篇
  2022年   112篇
  2021年   278篇
  2020年   325篇
  2019年   254篇
  2018年   220篇
  2017年   285篇
  2016年   257篇
  2015年   223篇
  2014年   463篇
  2013年   578篇
  2012年   441篇
  2011年   440篇
  2010年   389篇
  2009年   390篇
  2008年   368篇
  2007年   368篇
  2006年   414篇
  2005年   324篇
  2004年   315篇
  2003年   321篇
  2002年   284篇
  2001年   185篇
  2000年   182篇
  1999年   162篇
  1998年   110篇
  1997年   111篇
  1996年   129篇
  1995年   132篇
  1994年   88篇
  1993年   88篇
  1992年   80篇
  1991年   71篇
  1990年   60篇
  1989年   63篇
  1988年   61篇
  1987年   42篇
  1986年   19篇
  1985年   33篇
  1984年   27篇
  1983年   25篇
  1982年   16篇
  1981年   21篇
  1980年   32篇
  1979年   25篇
  1978年   17篇
  1976年   6篇
  1975年   2篇
  1974年   4篇
排序方式: 共有8931条查询结果,搜索用时 31 毫秒
81.
BACKGROUND: Male fertility largely depends on the quality of sperm production, which may be affected by environmental and genetic factors. In this study, we explored a possible role of the polymerase gamma (POLG) gene polymorphism, recently reported to be associated with male infertility in some populations. METHODS: The polymorphic CAG repeat (usually 10 codons long) in the POLG gene was studied in 1298 male subjects: 429 patients with infertility/subfertility, and 869 controls (495 men from the general population with unknown fertility and 374 recent fathers). In all subjects, the POLG polymorphism was assessed in relation to their semen quality, and--in the fertile controls--with biological fecundity measured as waiting time-to-pregnancy (TTP) for the couples. In the patients lacking the common POLG allele, the outcome of the assisted reproductive techniques (ART) for the couples was evaluated. RESULTS: The absence of one (10/ not equal to 10) or both common POLG alleles (not equal to 10/not equal to 10) was more frequent among the subfertile patients than among fertile controls (P=0.021 and P=0.04 respectively). The estimated predictive value for infertility in a man homozygous for the POLG polymorphism was 15.5% (95% CI: 4.8-51%). There was a positive association with sperm concentration: 14.3% of the normospermic subfertile patients were homozygous for the absence of the common POLG allele (not equal to 10/not equal to 10), in comparison with 2.3% of unselected controls (P=0.001) and 0.9% of the fertile men (P=0.0001). No association with sperm motility, morphology and TTP was found. Spermatozoa of the three not equal to 10/not equal to 10 patients treated with IVF retained the ability to penetrate the egg, but the fertilization rate was low. Nine homozygous not equal to 10/ not equal to 10 patients were treated with ICSI, resulting in pregnancy in seven couples. CONCLUSIONS: The POLG gene polymorphism should be considered as a possible contributing factor in patients with unexplained subfertility and normal spermiograms. The oocyte penetration ability of sperm may be partially impaired in the not equal to 10/not equal to 10 patients but most of them can be successfully treated with ICSI.  相似文献   
82.
While the appropriate method for the investigation of female infertility continues to be debated, the timing of the investigation has received less attention. The current approach is time-consuming, and paradoxically may lead to overtreatment as well as undertreatment. Recent findings on fecundity and the conception window in humans have important implications for the timing of the investigation of female infertility. The findings support the view that fertility-oriented intercourse may have a major impact in reducing the time to pregnancy. Procedures for the investigation of female infertility are becoming less invasive and more accurate, while the therapies for infertility are more effective. It is proposed that under appropriate circumstances female infertility should be investigated after 6 months of fertility-oriented intercourse.  相似文献   
83.
PROBLEM: The presence of antisperm antibodies (ASA) in males can reduce fecundity, however, relationship between the two is disputed. This study was performed to investigate if there is diversity of ASA bound to sperm surface using immunobead test (IBT) combined with complement dependent sperm immobilization test (SIT). METHODS: The ASA bound to sperm surface were detected using the direct IBT (D-IBT) in 275 semen samples. In some cases with ASA detected by D-IBT, sperm immobilizing antibodies bound to sperm surface were also evaluated using direct SIT (D-SIT). RESULTS: The incidence of the immunoglobulin G (IgG), IgA, and IgM classes of ASA detected by D-IBT were 2.5, 1.8, and 0.4%, respectively. Totally, nine (3.3%) infertile men had ASA on the sperm surface. D-SIT was tested positive in four (66.7%) of six cases with ASA assessed by D-IBT. CONCLUSIONS: Some of the sperm-bound antibodies are associated with complement dependent sperm immobilizing antibodies, indicating that there exists a heterogeneity of sperm-bound antibodies. This result might be one of the reasons for the controversy about the relationship between ASA and immunological infertility in men.  相似文献   
84.
BACKGROUND: Recent data emphasized the implication of polymerase gamma (POLG) CAG repeats in infertility, making it a very attractive gene for study. A comparison of POLG CAG repeats in infertile and fertile men showed a clear association between the absence of the usual 10-CAG allele and male infertility, excluding azoospermia. It has also been suggested that the POLG gene polymorphism should be considered as a possible contributing factor in unexplained couple infertility where semen parameters are normal. In this study, we investigated the POLG CAG repeats, in a well-defined population of patients with severe male factor infertility. METHODS: We conducted a large study of POLG CAG repeats in 433 infertile and 91 fertile, normozoospermic and healthy males. In all subjects, phenotypic data, including semen parameters, hormonal status and clinical profiles, were available. RESULTS: Thirteen 'homozygous mutants' (3%) were found among the 433 idiopathic infertile patients. The follow-up of the 13 'homozygous mutant' resulted in pregnancy for more than half of the couples, through assisted reproductive techniques or even spontaneously. In addition, one 'homozygous mutant' was identified in 91 fertile men (1.1%) CONCLUSION: Under our conditions, our study does not confirm any relationship between the polymorphic CAG repeat in the POLG gene and male infertility.  相似文献   
85.
Endometriosis is considered primarily a disease of the endometrial-subendometrial unit or archimetra. The clinical picture of endometriosis characterises this disease as a hyperactivation of genuine archimetrial functions such as proliferation, inflammatory defence and peristalsis. While the aetiology of the disease remains to be elucidated, a key event appears to consist in the local production of extraovarian oestrogen by a pathological expression of the P450 aromatase. The starting event may consist in a hyperactivity of the endometrial inflammatory defence, a hyperactivity of the endometrial oxytocin/oxytocin receptor system or in the pathological expression of the P450 aromatase system itself. Regardless of which of these levels the starting event is localized in, they influence each other on both the level of the archimetra and the endometriotic lesions. Locally elevated oestrogen levels inevitably up-regulate the endometrial oxytocin mRNA and increased levels of oxytocin result in uterine hyperperistalsis, increased transtubal seeding of endometrial tissue fragments and finally subfertility and infertility by impairment of the uterine mechanism of rapid and sustained sperm transport. Locally increased levels of oestrogen lead, on both the level of the endometrial-subendometrial unit and the endometriotic lesion, to processes of hyperproliferation. These processes result, on the level of the uterus, in an infiltrative growth of elements of the archimetra into the neometra and, on the level of the endometriotic lesion, in infiltrative endometriosis. There is circumstantial evidence that trauma might be an important initial event that induces the specific biochemical and cellular responses of the archimetra. This model is able to explain both the pleiomorphic appearance of endometriosis and the, up until now, enigmatic infertility associated with mild and moderate endometriosis.  相似文献   
86.
Infertility represents a major medical, economic, and psychological problem. Stem cells therapy for infertility has a great interest nowadays especially for cancer survivors at pre-reproductive and reproductive age.

 Thirty-two adult male albino rats were used, divided equally into four groups; Group I (Control group) received isotonic saline intraperitoneally (i.p.) as vehicle. Group II (Cisplatin-treated group) received Cisplatin (i.p.) at a single dose of 7 mg/kg, and then were sacrificed after 5 days. Group III (Stem-cell-treated group) received Cisplatin (i.p.) at a single dose of 7 mg/kg, then after 5 days received adipose-derived mesenchymal stem cells (ADMSCs) (1 × 106). Cells were injected in the rete testis, then after 60 days, the animals were sacrificed. Group IV (Auto healing group) received Cisplatin (i.p.) at a single dose of 7 mg/kg, and then left for 65 days then the animals were sacrificed. Cisplatin administration resulted in degenerative changes in the testicular architecture in the form of thickened irregular BM of seminiferous tubules. The germinal epithelium showed disorganization and marked reduction in the thickness, associated with Sertoli cells preservation. Features of apoptosis assured by elevated caspase-3 expression were noticed. The interstitium showed cellular infiltration and distorted Leydig cells. Injection of (ADMSCs) resulted in great improvement of testicular architecture and increase in the testosterone level associated with strong immune reaction of the CD-44. ADMSCs are recommended as a new treatment modality for male infertility.

Abbreviation: i.p.: intraperitoneally; BM: basement membrane; ADMSCs: adipose-derived mesenchymal stem cells; WHO: World Health Organization; MSCs: mesenchymal stem cells; DMEM: Dulbecco modified eagles media; PBS: phosphate-buffered saline; FACS: fluorescence-activated cell sorting; ELISA: enzyme-linked immunosorbent assay; CP: Cisplatin; ROS: reactive oxygen species; CAT: catalase; SOD: superoxide dismutase; OS: oxidative stress; SSCs: spermatogonia stem cells; GCs: germ cells; UCMSCs: umblical cord mesenchymal stem cells; TGFb1: transforming growth factor beta-1; BMP4: Bone morphogenic protein 4; BMP8b: bone morphogenic protein 8b.  相似文献   

87.
ABSTRACT: The ovarian histopathology of bitches immunized with crude (cPZP) or partially purified (pPZP) porcine zona pellucida proteins was examined in order to determine the cause of abnormal estrous cycles. The majority of immunized bitches had ovarian cytes. Those immunized with cPZP had follicular cysts lined with a thin layer of granulosa cells, while in those immunized with pPZP, the cysts were lined by a basement membrane with a clump of luteinized cells. In two bitches immunized with cPZP, oocytes were present only in primordial follicles. Similar abnormalities were not found in a bitch immunized with human serum albumin or in 12 untreated bitches. Oocytes flushed from the oviducts of mated, immunized bitches were degenerating, which may have been a primary cause of infertility in such bitches. Ovaries studied 2–6 weeks after immunization showed no loss of gap junctional communication between oocytes and granulosa cells, nor was any inflammatory reaction seen. IgG was bound to the zona as revealed by fluoresceinated protein A staining of frozen sections of those ovaries. Abnormal estrous cycles in PZP-immunized bitches appear to result from follicular dysgenesis or cyst formation, but the etiology of these conditions is unresolved.  相似文献   
88.
BACKGROUND: This study analyses the prevalence of karyotype changes and Yq11 microdeletions among couples referred for assisted reproduction techniques. METHODS: Prior to receiving either IVF or ICSI treatment, each partner of 2078 infertile couples was screened for karyotype changes by GTG-banding technique on peripheral lymphocytes. No subject presented with obvious phenotype of chromosomal rearrangement. All the oligo/azoospermic men with normal karyotype were further investigated by PCR for Yq11 microdeletions. RESULTS: Eighty-two out of 2078 couples (3.95%) had one partner carrying a chromosomal change, and 10 out of 202 (4.95%) men showed Yq11 microdeletions. The chromosomal rearrangements were 44 (2.1%) translocations, 23 (1.1%) gonosomal mosaics, six (0.3%) 47,XXY, five (0.24%) marker chromosomes, three (0.14%) inversions and one (0.05%) duplication. Frequency of anomalies in men and women were similar: 42 and 40 cases respectively. CONCLUSIONS: Partners of infertile couples requiring IVF or ICSI treatment appear to be affected by higher frequency of chromosomal rearrangements than the general population. Categories with greater risk were represented by men with sperm cell count <20 x 10(6) sperm/ml, and women with history of pregnancy loss.  相似文献   
89.
诱导供者特异性免疫耐受是最终克服移植排斥提高受者生存质量的有效途径之一。近年随着对树突状细胞发育成熟过程的认识步步深入,树突状细胞在移植排斥和移植耐受平衡中的双向调节作用引入注目。  相似文献   
90.
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