全文获取类型
收费全文 | 1459篇 |
免费 | 134篇 |
国内免费 | 12篇 |
专业分类
耳鼻咽喉 | 11篇 |
儿科学 | 28篇 |
妇产科学 | 13篇 |
基础医学 | 204篇 |
口腔科学 | 16篇 |
临床医学 | 289篇 |
内科学 | 262篇 |
皮肤病学 | 5篇 |
神经病学 | 141篇 |
特种医学 | 131篇 |
外科学 | 107篇 |
综合类 | 52篇 |
预防医学 | 125篇 |
眼科学 | 4篇 |
药学 | 146篇 |
中国医学 | 2篇 |
肿瘤学 | 69篇 |
出版年
2023年 | 10篇 |
2022年 | 11篇 |
2021年 | 18篇 |
2018年 | 19篇 |
2017年 | 19篇 |
2016年 | 15篇 |
2015年 | 24篇 |
2014年 | 39篇 |
2013年 | 47篇 |
2012年 | 41篇 |
2011年 | 44篇 |
2010年 | 36篇 |
2009年 | 28篇 |
2008年 | 49篇 |
2007年 | 36篇 |
2006年 | 40篇 |
2005年 | 32篇 |
2004年 | 43篇 |
2003年 | 35篇 |
2002年 | 40篇 |
2001年 | 46篇 |
2000年 | 38篇 |
1999年 | 51篇 |
1998年 | 35篇 |
1997年 | 27篇 |
1996年 | 35篇 |
1995年 | 27篇 |
1994年 | 24篇 |
1993年 | 23篇 |
1992年 | 48篇 |
1991年 | 34篇 |
1990年 | 48篇 |
1989年 | 45篇 |
1988年 | 50篇 |
1987年 | 50篇 |
1986年 | 41篇 |
1985年 | 49篇 |
1984年 | 32篇 |
1983年 | 33篇 |
1982年 | 20篇 |
1981年 | 9篇 |
1980年 | 15篇 |
1979年 | 16篇 |
1978年 | 22篇 |
1977年 | 19篇 |
1976年 | 14篇 |
1975年 | 14篇 |
1974年 | 19篇 |
1971年 | 14篇 |
1970年 | 15篇 |
排序方式: 共有1605条查询结果,搜索用时 15 毫秒
21.
Carolyn R. Durham Hong Zhu Bettie Sue S. Masters Evan R. Simpson Carole R. Mendelson 《Molecular and cellular endocrinology》1985,40(2-3):211-219
Aromatase is an enzyme complex that is composed of a specific form of cytochrome P-450 and a flavoprotein, NADPH-cytochrome P-450 reductase. Aromatase activity of granulosa cells is increased markedly by follicle-stimulating hormone (FSH) and by analogs of cyclic AMP. It was the objective of the present study to investigate the effects of FSH and dibutyryl cyclic AMP (Bt2cAMP) on the synthesis of NADPH-cytochrome P-450 reductase in rat granulosa cells maintained in vitro. Granulosa cells were obtained from the ovaries of diethylstilbestrol (DES)-treated immature rats and were incubated in the presence of DES (10−7 M), DES + FSH (250 ng/ml), or DES + Bt2cAMP (1 mM) for up to 72 h. After 72 h of incubation, aromatase activity of cells incubated with DES alone was 5 pmoles estrogen formed 2 h−1 mg−1 protein and was increased > 60-fold in cells incubated with FSH or Bt2cAMP. NADPH-cytochrome P-450 reductase was immunoisolated from [35S]methionine-labeled lysates of granulosa cells incubated for 72 h in the absence or presence of stimulatory factors. The rate of synthesis of reductase was found to be increased about 3-fold in cells incubated with DES + FSH or DES + Bt2cAMP as compared to cells incubated with DES alone. By immunoblot analysis we found that the cellular content of reductase was increased about 2-fold by FSH and Bt2cAMP treatment. Reductase specific activity was 10 nmoles min−1 mg−1 protein in membrane fractions of DES-treated cells and was increased 1.6-fold by FSH treatment. These findings are indicative that FSH increases the rate of synthesis, cellular content and specific activity of NADPH-cytochrome P-450 reductase in rat granulosa cells in vitro. The finding that Bt2cAMP causes a similar induction of reductase synthesis is suggestive that the stimulatory effect of FSH on this component of the aromatase enzyme complex is mediated by an increase in cyclic AMP formation. 相似文献
22.
23.
Background Aging of the midface is complex and poorly understood. Changes occur not only in the facial soft tissues, but also in the
underlying bony structure. Computed tomography (CT) imaging was used for investigating characteristics of the bony orbit and
the anterior wall of the maxilla in patients of different ages and genders.
Methods Facial CT scans were performed for 62 patients ranging in age from 21 to 70 years, who were divided into three age groups:
21–30 years, 41–50 years, and 61–70 years. Patients also were grouped by gender. The lengths of the orbital roof and floor and
the angle of the anterior wall of the maxilla were recorded on parasagittal images through the midline of the orbit for each
patient.
Results The lengths of the orbital roof and floor at their midpoints showed no significant differences between the age groups. When
grouped by gender, the lengths were found to be statistically longer for males than for females. The angle between the anterior
maxillary wall and the orbital floor was found to have a statistically significant decrease with advancing age among both
sexes.
Conclusion Bony changes occur in the skeleton of the midcheek with advancing age for both males and females. The anterior maxillary wall
retrudes in relation to the bony orbit, which maintains a fixed anteroposterior dimension at its midpoint. These changes should
be considered in addressing the aging midface. 相似文献
24.
Kremer CL Klein RR Mendelson J Browne W Samadzedeh LK Vanpatten K Highstrom L Pestano GA Nagle RB 《The Prostate》2006,66(11):1203-1212
BACKGROUND: The PI3K/AKT/mTOR pathway is central to prostate cancer progression. A preliminary investigation of immuno-histochemical expression of mammalian target of rapamycin (mTOR) pathway markers was undertaken to identify patterns of expression in prostate tissue. METHODS: Immunohistochemistry was performed on a custom-made prostate tissue array. Mean long scores and variability of long scores for each marker were recorded for normal lumenal cells, prostate intraepithelial neoplasia (PIN), and cancer. RESULTS: Expression of PTEN decreased and mTOR signaling pathway markers increased in PIN and in cancer as compared to normal cells in the majority of samples. Overexpression of 4E-BP1 and p-4E-BP1 was observed in PIN and cancer. However, in cancer, the overexpression of 4E-BP1 was significantly higher than with any other marker. DISCUSSION: Results suggest that 4E-BP1 overexpression is strongly associated with prostate cancer, especially when combined with PTEN and mTOR expression data. Hierarchical clustering analysis utilizing PTEN, mTOR, and 4E-BP1 separated normal from cancer cell populations in most cases. 相似文献
25.
W H Cleland C R Mendelson E R Simpson 《The Journal of clinical endocrinology and metabolism》1985,60(1):174-177
Adipose tissue is the principal site of estrogen formation in postmenopausal women; with advancing age as well as with increased body weight, there is an increase in the fractional conversion of circulating androstenedione to estrone. We have studied the effects of aging as well as body weight on aromatase activity of adipose tissue specimens taken from 50 women of various ages and weights. Since aromatase activity of adipose tissue is detectable primarily in stromal cells, these cells were incubated with [1-3H]androstenedione (150 nM), and estrogen formation was assayed by measuring the incorporation of tritium into [3H]water. The aromatization rate, when normalized on the basis of equal numbers of cells, increased with increasing age (P less than 0.03; r = 0.43). In contrast, when expressed as a function of body weight, no change in aromatase activity of adipose stromal cells were found. Aromatization of androstenedione by cells from young women who had undergone oophorectomy was not increased compared with that of cells from young women with normal ovarian function, indicating that the onset of menopause per se and the accompanying increase in circulating gonadotropin levels were not causative factors in the increased aromatase activity of adipose stromal cells. We conclude, therefore, that increased estrone production associated with aging may result from an increase in the specific activity of the aromatase enzyme in adipose stromal cells and is not affected by changes in gonadotropin concentrations associated with menopause. On the other hand, the increase in estrogen formation as a function of obesity is probably due to increased numbers of adipose cells, rather than to an increase in the specific activity of aromatase in those cells. 相似文献
26.
27.
Angela Huttner Alice Bricheux Carianne J.M. Buurmeijer-van Dijk Matthew Harvey Alison Holmes Britta Lassmann Valéry Lavergne Alexandra Mailles Marc Mendelson Nicolas Muller Maurizio Sanguinetti Cynthia Sears Chrysanthi Skevaki Uzma Syed Salandra Thomas Talia H. Swartz Talia H. Swartz 《Clinical microbiology and infection》2021,27(5):704-707
BackgroundThough women increasingly make up the majority of medical-school and other science graduates, they remain a minority in academic biomedical settings, where they are less likely to hold leadership positions or be awarded research funding. A major factor is the career breaks that women disproportionately take to see to familial duties. They experience a related, but overlooked, hurdle upon their return: they are often too old to be eligible for ‘early-career researcher’ grants and ‘career-development’ awards, which are stepping stones to leadership positions in many institutions and which determine the demographics of their hierarchies for decades to come. Though age limits are imposed to protect young applicants from more experienced seniors, they have an unintended side effect of excluding returning workers, still disproportionately women, from the running.MethodsIn this joint effort by the European Society of Clinical Microbiology and Infectious Diseases, the Federation of European Microbiological Societies, the Infectious Disease Society of America, the International Society for Infectious Diseases and the Swiss Society for Infectious Diseases, we invited all European Congress of Clinical Microbiology and Infectious Diseases-affiliated medical societies and funding bodies to participate in a survey on current ‘early-career’ application restrictions and measures taken to provide protections for career breaks.RecommendationsThe following simple consensus recommendations are geared to funding bodies, academic societies and other organizations for the fair handling of eligibility for early-career awards: 1. Apply a professional, not physiological, age limit to applicants. 2. State clearly in the award announcement that career breaks will be factored into applicants' evaluations such that: ? Time absent is time extended: for every full-time equivalent of career break taken, the same full-time equivalent will be extended to the professional age limit. ? Opportunity costs will also be taken into account: people who take career breaks risk additional opportunity costs, with work that they did before the career break often being forgotten or poorly documented, particularly in bibliometric accounting. Although there is no standardized metric to measure additional opportunity costs, organizations should (a) keep in mind their existence when judging applicants' submissions, and (b) note clearly in the award announcement that opportunity costs of career breaks are also taken into account. 3. State clearly that further considerations can be undertaken, using more individualized criteria that are specific to the applicant population and the award in question.The working group welcomes feedback so that these recommendations can be improved and updated as needed. 相似文献
28.
Hemostatic plug (HP) formation was investigated in the ear bleeding time incision in normal and von Willebrand pigs. HP volume was calculated by integrating the areas of serial sections. In normal pigs (n = 11), platelets immediately formed a layer on the surface of the cut channel. Platelet aggregates formed at the ends of transected vessels and gradually enlarged. Finally, all transected vessels were occluded by HP and bleeding stopped. In contrast, large HPs were formed in the incision in von Willebrand's disease (vWD) pigs (n = 4); these HPs did not cover the ends of the transected vessels, which continued to bleed, allowing the formation of large hemostatically ineffective platelet aggregates in the incision. Canals traversed these HPs, and bleeding from the open vessels may have continued through them. After infusion of cryoprecipitate into a vWD pig, the bleeding time shortened, and the morphological findings of the HPs were similar to those of normal pigs. In normal pigs (n = 3) infused with an anti- Willebrand factor monoclonal antibody, which prolonged the bleeding time, a large HP formed in the incision, similar to that observed in the vWD pig. The volume of the normal and vWD HPs increased with time. These in vivo findings suggest that Willebrand factor is involved in the localization of the HP to the damaged vessel and may also play a role in platelet-platelet interaction. A computerized morphometric technique was used for measuring the volume of the hemostatic plugs and the distance of sequential points on the perimeter of the HP from the center of selected bleeding vessels. 相似文献
29.
30.