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   4803篇
  免费   344篇
  国内免费   156篇
耳鼻咽喉   17篇
儿科学   121篇
妇产科学   659篇
基础医学   618篇
口腔科学   81篇
临床医学   322篇
内科学   433篇
皮肤病学   52篇
神经病学   182篇
特种医学   58篇
外国民族医学   3篇
外科学   609篇
综合类   676篇
预防医学   242篇
眼科学   40篇
药学   700篇
  2篇
中国医学   161篇
肿瘤学   327篇
  2023年   49篇
  2022年   77篇
  2021年   148篇
  2020年   133篇
  2019年   119篇
  2018年   119篇
  2017年   155篇
  2016年   156篇
  2015年   173篇
  2014年   269篇
  2013年   456篇
  2012年   243篇
  2011年   240篇
  2010年   215篇
  2009年   204篇
  2008年   183篇
  2007年   210篇
  2006年   181篇
  2005年   180篇
  2004年   162篇
  2003年   171篇
  2002年   130篇
  2001年   132篇
  2000年   105篇
  1999年   84篇
  1998年   83篇
  1997年   55篇
  1996年   80篇
  1995年   76篇
  1994年   59篇
  1993年   63篇
  1992年   50篇
  1991年   46篇
  1990年   44篇
  1989年   49篇
  1988年   38篇
  1987年   29篇
  1986年   30篇
  1985年   42篇
  1984年   36篇
  1983年   28篇
  1982年   28篇
  1981年   21篇
  1980年   25篇
  1979年   28篇
  1978年   15篇
  1977年   20篇
  1976年   22篇
  1975年   17篇
  1974年   12篇
排序方式: 共有5303条查询结果,搜索用时 31 毫秒
41.
The study objectives were to compare in vitro transportability and physical properties of respiratory mucus, obtained invasively by direct collection (DC) right after endotracheal intubation and non-invasively by sputum induction with 3% hypertonic saline solution inhalation (SI) 24 h before the anesthesia. Twenty-two patients with no pulmonary disease scheduled for elective abdominal surgical procedures were studied. The parameters analyzed and the main results are as follows. (1) Transportability by cilia (MCT), SI was higher than DC (0.94+/-0.25 and 0.62+/-0.25; P<0.001). There was a significant correlation between the two methods and DC could be estimated by: DC=0.21+(0.44 SI) (r=0.44; P<0.001). (2) Transportability by cough (CC), SI was higher than DC (68.23+/-32.1 and 33.58+/-19.04 mm; P=0.002). (3) Contact angle (CA), SI was lower than DC (10+/-3 degrees and 22+/-14 degrees ; P=0.025). (4) Rheological properties (no significant difference obtained between SI and DC). These results indicated that SI changes mucus physical properties and transportability in non-expectorators.  相似文献   
42.
Ovulation induction is the method for treating anovulatory infertility. For patients with hypogonadotrophic hypogonadism, the treatment involves administration of both FSH and LH, while HCG is injected for follicle rupture. Pulsatile GnRH has the same effectiveness as gonadotrophins and the advantage of the low multiple pregnancy rate. In polycystic ovary syndrome (PCOS), the first treatment choice is clomiphene citrate. With this drug, in properly selected patients, the cumulative pregnancy rate approaches that of normal women. Low-dose protocols of FSH are the second line of treatment, effective in inducing monofollicular development. Laparoscopic ovarian drilling can be an alternative but not as a first choice treatment in clomiphene-resistant patients. Other treatments, such as pulsatile GnRH and GnRH agonists, are hardly used today in PCOS. However, in obese women with PCOS, weight loss and exercise should be recommended as the first line of therapy. Newer agents including aromatase inhibitors and insulin sensitizers, although promising, need further evaluation.  相似文献   
43.
The focus of regenerative medicine is rebuilding damaged tissues by cell transplantation or implantation of bioartificial tissues. In either case, therapies focus on adult stem cells (ASCs) and embryonic stem cells (ESCs) as cell sources. Here we review four topics based on these two cell sources. The first compares the current performance of ASCs and ESCs as cell transplant therapies and the drawbacks of each. The second explores somatic cell nuclear transfer (SCNT) as a method to derive ESCs that will not be immunorejected. The third topic explores how SCNT and ESC research has led to the ability to derive pluripotent ESCs by the dedifferentiation of adult somatic cells. Lastly, we discuss how research on activation of intrinsic adult stem cells and on somatic cell dedifferentiation can evolve regenerative medicine from a platform consisting of cell transplantation to one that includes the chemical induction of regeneration from the body's own cells at the site of injury. Developmental Dynamics 237:3648–3671, 2008. © 2008 Wiley‐Liss, Inc.  相似文献   
44.
To investigate the effect of co-treatment with growth hormone(GH) for ovulation induction with human menopausal gonadotrophins(HMG) on conception, we compared the pregnancy rate and responseto co-treatment with GH versus HMG/human chorionic gonadotrophin(HCG) alone in a prospective, randomized, cross-over protocolof volation induction for either in-vivo or in-vitro fertilization(IVF). The main outcome measures were the amount of gonadotrophinused and conception. Co-treatment with GH was associated witha reduction of 30% in gonadotrophin requirement. In 24 clonidinenegative patients 14 pregnancies were achieved (58.3%) eitherin the GH/HMG/HCG cycle or in the succeeding one. GH co-treatmentdid not generate any pregnancy in eight clonidine positive patients.We conclude that growth hormone may increase the pregnancy ratewhen combined with HMG/HCG for ovulation induction, not onlyin the co-treatment cycle but also in the succeeding one. Thebeneficial, synergistic effect of GH co-treatment was detectedin clonidine negative but not in clonidine positive infertilepatients.  相似文献   
45.
46.
High risk pregnancies in hypopituitary women   总被引:1,自引:0,他引:1  
BACKGROUND: Various short papers have suggested that pregnancies in women with hypopituitarism are high risk but no formal assessment of pregnancy outcome has yet been reported. METHODS: An audit was carried out concerning the outcome of 18 pregnancies in nine women who underwent ovulation induction in a single centre over 20 years. RESULTS: The live birth rate was 61%, miscarriage rate 28% and mid-trimester uterine death rate 11% with no survivors from four sets of twins. The Caesarian section rate was 100% and half of the live births were on or below the 10th centile for weight. One woman successfully breast-fed. CONCLUSIONS: Women with hypopituitarism have high-risk pregnancies, perhaps because of a uterine defect secondary to endocrine deficiency. Fertility treatment must strive for singleton pregnancies with application of particularly strict criteria to avoid twin pregnancies. Early elective Caesarian section is probably warranted in this group.  相似文献   
47.
Objectives: To look for possible association between past history of ovulation induction and age at menopause. Design: Women attending our postmenopausal outpatient clinic were asked to fill questionnaires with demographic data, obstetrical history (including treatment for infertility), and medical details related to menopause. Patients: The study group (n=31) consisted of women with a history of ovulation induction, and a control group (n=200) included women who did not experience such intervention. Results: The age at the final menstrual bleeding was 46.4±5 in the study group, and 50±4 for the control group (P<0.001). This difference was most prominent for women who had induction of ovulation prior to age 35 years: they entered menopause at age 43.8±5 years. Smoking had a weak effect on the age at menopause (48.5±4 for current, vs. 49.9±4 for non- or past-smokers; P<0.03). Conclusions: This retrospective and preliminary study raises the question whether hormonal manipulations and ovarian over-stimulation during fertility treatments could be a risk factor for premature menopause.  相似文献   
48.
Newcastle disease virus (NDV) has received much attention recentlybecause of its non-specific immune stimulating potential andits various anti-tumor activities. Here we describe that NDVinduces synthesis of NO and causes an activation of nuclearfactor-kB (NF-kB) In murine macrophages. These reactions werepart of an activation process which included also stimulationof adenosine deaminase and inhibition of 5'-nucleotidase. NDV-mediatedNO synthesis and NF-kB activation were blocked by an antioxidant(butylated hydroxyanisole), by an inhibitor of protein tyrosinekinase (genistein) and of protein kinase A (H-89), but not byan inhibitor of protein kinase C (staurosporin). These datasuggest that signalling requirements of NF-kB activation andNO production in NDV-treated macrophages are similar.  相似文献   
49.
Induction of ovulation after gnRH antagonists   总被引:2,自引:0,他引:2  
The gonadotrophin-releasing hormone (GnRH) antagonist binds competitively to the receptors and thereby prevents endogenous GnRH from exerting its stimulatory effect on the pituitary cells. This causes suppression of gonadotrophin secretion which occurs immediately after administration of the antagonist. When using GnRH antagonist in controlled ovarian stimulation, ovulation or maturation of the oocyte can, therefore, be induced by a variety of drugs, e.g. native GnRH, recombinant LH or short-acting GnRH agonists. Short-acting GnRH agonists were recommended for triggering ovulation in cases with a high risk of developing ovarian hyperstimulation syndrome (OHSS). Since it is evident that GnRH is required to initiate the LH surge and the oestradiol rise, a single administration of GnRH antagonist during the late follicular phase delays the LH surge. Studies showed that a single s.c. administration of 3 or 5 mg of Cetrorelix in the late follicular stage was sufficient to prevent the LH surge for 617 days. This phenomenon can be used in high responder patients who are prone to OHSS. The question whether this delay has any effect on oocyte quality and maturation still remains unanswered. Overall, there are four uses for GnRH antagonist: (i) using short-acting GnRH agonists for triggering ovulation in cases in which the GnRH antagonist is part of the protocol for ovarian stimulation. Recombinant LH and native LHRH could also be used as triggers of LH surge; (ii) delaying the LH surge in cases prone to OHSS by treatment with GnRH antagonist; (iii) to administer GnRH antagonist during the luteal phase to decrease the activity of corpora lutea; (iv) in polycystic ovarian disease with elevated LH the LH/FSH ratio can be corrected with the injection of GnRH antagonist prior to and during ovarian stimulation.  相似文献   
50.
In this study we utilized the hamster ovary as a model to investigatethe effects of ovulation induction with gonadotrophin on theactivation of the signal transducer effector system, adenylylcyclase (AC). For this purpose, we prepared membrane particlesfrom the ovary and analysed both gonadotrophin-sensitive ACand non-receptor-mediated activation during a cycle in whichovulation and luteinization were achieved by pregnant mare’sserum gonadotrophin (PMSG)/human chorionic gonadotrophin (HCG)administration. Results were directly compared with AC activationin similarly prepared membranes obtained at different stagesof the natural unstimulated cycle. AC activity was quantifiedby the direct conversion of ATP substrate into cyclic adenosinemonophosphate (cAMP). Measurements of ovarian weights, serumoestradiol and progesterone concentrations provided a solidbase from which to evaluate the functional status of the ovaryat each time period during the natural and stimulated cycles.We found that ovarian membranes contain functional componentsof the AC system and demonstrated that AC is highly dependenton hormonal changes and the functional state of the ovary. Thus,during the natural cycle, ovarian AC showed relatively constantresponsiveness to follicle-stimulating hormone (FSH) throughoutthe cycle, whereas responsiveness to luteinizing hormone (LH)/HCGreached its peak during the luteal phase. On the other hand,during the stimulated cycle, sensitivity to FSH and LH/HCG variedconsiderably, being absent during the peri-ovulatory period.AC responsiveness to gonadotrophins was only regained 48 h afterovulation. Also during the peri-ovulatory period of the gonadotrophin-inducedcycle, stimulation of ovarian AC with non-hormonal activatorsdeclined. However, the rate of cAMP production in response tothese activators remained very high, indicating that despiterefractoriness to gonadotrophins, ovarian AC retained the capacityto generate cAMP at near maximal efficiency. Basal (non-stimulated)activity, guanine nucleotide activation, hormone responsivenessand stimulation by the non-hormonal activators NaF and forskolinwere all significantly increased in comparison with the naturalcycle. Basal activity alone was 7-fold higher than the activityobserved during the unstimulated cycle. These results suggestthat subsequent to exogenous gonadotrophin administration, thetransmembrane effector AC system must be primed for a higherlevel of activity in the ovarian tissue. This priming of theovarian AC system by exogenous gonadotrophin was also evidentwhen the enzyme was measured under conditions allowing maximalactivity, i.e. in the presence of a combination of NaF and forskolin.Maximal AC activity increased 4- to 5-fold compared with thenatural cycle. We conclude that gonadotrophin administrationinducing ovulation causes profound alterations in the expressionof AC in ovarian membranes. Gonadotrophin treatment increasedthe enzyme activity and induced a temporal desensitization toFSH and LH/HCG in the peri-ovulatory period of the stimulatedcycle. Because the gonadotrophin-sensitive AC system representsthe capacity of FSH and LH/HCG receptors to couple and elicita biological response, our results provide new insights intothe cellular mechanisms that regulate ovarian activity duringinduction of ovulation.  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