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   2182篇
  免费   246篇
  国内免费   17篇
耳鼻咽喉   7篇
儿科学   88篇
妇产科学   45篇
基础医学   239篇
口腔科学   41篇
临床医学   227篇
内科学   375篇
皮肤病学   18篇
神经病学   234篇
特种医学   213篇
外科学   305篇
综合类   95篇
一般理论   4篇
预防医学   147篇
眼科学   39篇
药学   124篇
  1篇
肿瘤学   243篇
  2021年   46篇
  2020年   27篇
  2019年   39篇
  2018年   38篇
  2017年   28篇
  2016年   29篇
  2015年   31篇
  2014年   46篇
  2013年   52篇
  2012年   64篇
  2011年   86篇
  2010年   64篇
  2009年   47篇
  2008年   58篇
  2007年   100篇
  2006年   71篇
  2005年   84篇
  2004年   80篇
  2003年   91篇
  2002年   80篇
  2001年   81篇
  2000年   76篇
  1999年   43篇
  1998年   49篇
  1997年   43篇
  1996年   30篇
  1995年   37篇
  1994年   32篇
  1993年   50篇
  1992年   37篇
  1991年   49篇
  1990年   50篇
  1989年   45篇
  1988年   45篇
  1987年   70篇
  1986年   42篇
  1985年   43篇
  1984年   32篇
  1983年   32篇
  1982年   19篇
  1981年   32篇
  1980年   27篇
  1979年   33篇
  1978年   33篇
  1977年   27篇
  1976年   20篇
  1975年   20篇
  1974年   27篇
  1973年   26篇
  1971年   14篇
排序方式: 共有2445条查询结果,搜索用时 31 毫秒
61.
62.
63.
64.
65.
Objective: To determine the perceived needs of perimenopausal women regarding the management of menopause and the resource needs of the clinicians who treat them. Setting: A large staff and group network model health maintenance organization (HMO) in New England. Participants: A random sample of 790 perimenopausal women aged 45–60 years who were members of the HMO in 1991, and a random sample of 180 clinicians in internal medicine, family practice, and obstetrics/gynecology practicing in the HMO during 1991. Method: Mailed surveys of women and clinicians were designed to assess possible needs and attitudes that could lead to the improvement of care for menopausal women. The chi-square test was used to determine differences in perceived needs and satisfaction levels among women with differences in self-reported menopausal status. The Kruskal-Wallis one-way analysis of variance and the Mann-Whitney U test were used in the clinician survey to test for differences among specialties and between genders. Results: The key findings include that: 1) most (81%) of the women wanted to see a woman clinician, 2) many (50%) were interested in a menopause support group, 3) 30% reported that their care for menopause had been fair to poor, 4) only 55% of the primary care specialists (including internal medicine and family practice) reported high confidence in their abilities to treat menopause, compared with 68% of the obstetric/gynecology clinicians, and 5) 56% of the clinicians surveyed said that support from the HMO to their practices for the treatment of menopause was fair to poor. Conclusions: There is an opportunity for better care for perimenopausal women as reported by two sources, HMO clinicians and members. To provide this care, clinicians may need explicit guidelines as well as administrative supports such as educational materials and specialty access. Since the capability for menopausal care from clinicians in obstetrics/gynecology is perceived to be higher than that from primary care clinicians, an opportunity for cross-specialty collaboration and training may exist.  相似文献   
66.
Adler  A; Albo  V; Blatt  J; Whiteside  TL; Herberman  RB 《Blood》1989,74(5):1690-1697
Activation and expansion in culture with rIL-2 of peripheral blood (PB) and/or bone marrow (BM) specimens derived from children with ALL and ANLL, with active disease (AP) and in remission were studied (RP). Baseline NK cytolytic activity from AP was found to be depressed, whereas RP-derived cells had normal NK activity, as assayed against K562 targets. Culture in rIL-2 significantly enhanced the NK activity of both AP- and RP-derived cells and generated LAK activity, as assayed by 4-hour 51Cr release, against NK-resistant Raji cell line and against fresh, allogeneic, and autologous tumor cells. Lytic activity against fresh, cryopreserved leukemia blasts was of lower than that found against cell lines. In three patients higher lytic activity against autologous than against allogeneic blasts was demonstrated. Expansion in culture with rIL-2 varied from twofold to 120-fold. rIL-2 activation and expansion was better in RP than in AP. The predominant phenotype of activated cells, as determined by flow cytometry, was [mean % (SD)]: CD3- = 54 (12), CD8+ = 55 (17), and NKH1+ = 26 (7). The consistently high level of CD8+ cells was accompanied by very low levels of CD4+ cells: mean = 11% (14). Double-marker analysis showed mean of 33% (10) for CD3+/NKH1+ cells and mean = 32 (11) for CD8+/NKH1+ cells, implying that these populations were overlapping. Kinetics of expression of cell surface markers during 2 to 3 weeks in culture showed that CD8+ and NKH1+ enrichment occurred during the first week and lasted for up to 4 weeks, whereas CD4+ expression decreased after the second week. A significant decrease in the expression of IL-2 receptors (CD25) was observed from the second week of culture. This study shows the feasibility of in vitro generation of killer cells from PB and BM of pediatric leukemia patients.  相似文献   
67.
Parallel measurements of the thermodynamics(free-energy, enthalpy, entropy and heat-capacity changes) of ligand binding toFK506 binding protein (FKBP-12) in H2O and D2O have been performed in an effortto probe the energetic contributions of single protein-ligand hydrogen bondsformed in the binding reactions. Changing tyrosine-82 to phenylalanine inFKBP-12 abolishes protein-ligand hydrogen bond interactions in the FKBP-12complexes with tacrolimus or rapamycin and leads to a large apparent enthalpicstabilization of binding in both H2O and D2O. High-resolution crystallographicanalysis reveals that two water molecules bound to the tyrosine-82 hydroxylgroup in unliganded FKBP-12 are displaced upon formation of the protein-ligandcomplexes. A thermodynamic analysis is presented that suggests that the removalof polar atoms from water contributes a highly unfavorable enthalpy change tothe formation of C=O...HO hydrogen bonds as they occur in the processes ofprotein folding and ligand binding. Despite the less favorable enthalpy change,the entropic advantage of displacing two water molecules upon binding leads to aslightly more favorable free-energy change of binding in the reactions withwild-type FKBP-12.  相似文献   
68.
Positive allosteric modulators (PAMs) of the mu-opioid receptor (MOR) have been hypothesized as potentially safer analgesics than traditional opioid drugs. This is based on the idea that PAMs will promote the action of endogenous opioid peptides while preserving their temporal and spatial release patterns and so have an improved therapeutic index. However, this hypothesis has never been tested. Here, we show that a mu-PAM, BMS-986122, enhances the ability of the endogenous opioid Methionine-enkephalin (Met-Enk) to stimulate G protein activity in mouse brain homogenates without activity on its own and to enhance G protein activation to a greater extent than β-arrestin recruitment in Chinese hamster ovary (CHO) cells expressing human mu-opioid receptors. Moreover, BMS-986122 increases the potency of Met-Enk to inhibit GABA release in the periaqueductal gray, an important site for antinociception. We describe in vivo experiments demonstrating that the mu-PAM produces antinociception in mouse models of acute noxious heat pain as well as inflammatory pain. These effects are blocked by MOR antagonists and are consistent with the hypothesis that in vivo mu-PAMs enhance the activity of endogenous opioid peptides. Because BMS-986122 does not bind to the orthosteric site and has no inherent agonist action at endogenously expressed levels of MOR, it produces a reduced level of morphine-like side effects of constipation, reward as measured by conditioned place preference, and respiratory depression. These data provide a rationale for the further exploration of the action and safety of mu-PAMs as an innovative approach to pain management.

Mu-opioid receptor (MOR) agonists are the most effective treatments for moderate to severe acute and chronic pain, yet their use is limited by serious side effects, including constipation, respiratory depression, and physical and psychological dependence. These side effects are on-target effects (MOR-mediated) and result from the wide distribution of MORs across the central nervous system (CNS) (1, 2). Safer pain therapies are desperately needed. However, because of the efficacy of MOR agonists in blocking pain, this receptor continues to be a primary target for the discovery of novel pain therapies. Unfortunately, most drug discovery programs involve designing compounds that bind to the orthosteric site on MOR—the site that binds endogenous opioid peptides as well as exogenous opioids. Not surprisingly, these newer drugs tend to exhibit qualitatively similar side effect profiles to traditional opioid analgesics.As an alternative, we have discovered small molecule, positive allosteric modulators of MOR [mu-PAMs (3)], including BMS-986122 (SI Appendix, Fig. S1). Such compounds interact with a site on MOR that is spatially distinct from the orthosteric site (37). Across a variety of in vitro assays, mu-PAMs increase the affinity and/or potency of orthosteric agonists at MOR, including exogenous MOR agonists as well as the endogenous opioid peptides Leucine- and Methionine-enkephalin, endomorphin-1, and β-endorphin (3, 8).These in vitro studies have led to development of a so-far untested hypothesis that in vivo, mu-PAMs will promote the activity of endogenous opioid peptides released during pain (911). If this hypothesis is correct, mu-PAMs could replace traditional opioids by boosting the body’s own natural response to pain to provide clinically meaningful analgesia. In support of this concept, so called “enkephalinase inhibitors” that prolong the lifetime of endogenous opioid peptides are effective in the management of pain in preclinical and clinical studies (1214), although such compounds are not selective for opioid peptides. Since mu-PAMs do not alter peptide release or metabolism, they should be more selective than enkephalinase inhibitors and also preserve the natural spatial and temporal release of the peptides in vivo following injury and/or during pain. To test this hypothesis, we examined the antinociceptive effects of BMS-986122 in mouse models of acute and inflammatory pain using measures of pain-evoked and pain-depressed behaviors as well as opioid side effects and the potential role of endogenous opioid peptides in these responses.  相似文献   
69.
Articular cartilage has a limited capacity to heal and, currently, no treatment exists that can restore normal hyaline cartilage. Creating tissue engineering scaffolds that more closely mimic the native extracellular matrix may be an attractive approach. Glycosaminoglycans, which are present in native cartilage tissue, provide signalling and structural cues to cells. This study evaluated the use of a glycosaminoglycan mimetic, derived from cellulose, as a potential scaffold for cartilage repair applications. Fully sulfated sodium cellulose sulfate (NaCS) was initially evaluated in soluble form as an additive to cell culture media. Human mesenchymal stem cell (MSC) chondrogenesis in pellet culture was enhanced with 0.01% NaCS added to induction media as demonstrated by significantly higher gene expression for type II collagen and aggrecan. NaCS was combined with gelatine to form fibrous scaffolds using the electrospinning technique. Scaffolds were characterized for fibre morphology, overall hydrolytic stability, protein/growth factor interaction and for supporting MSC chondrogenesis in vitro. Scaffolds immersed in phosphate buffered saline for up to 56 days had no changes in swelling and no dissolution of NaCS as compared to day 0. Increasing concentrations of the model protein lysozyme and transforming growth factor‐β3 were detected on scaffolds with increasing concentrations of NaCS (p < 0.05). MSC chondrogenesis was enhanced on the scaffold with the lowest NaCS concentration as seen with the highest collagen type II production, collagen type II immunostaining, and expression of cartilage‐specific genes. These studies demonstrate the feasibility of cellulose sulfate as a scaffolding material for cartilage tissue engineering. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   
70.
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