全文获取类型
收费全文 | 33017篇 |
免费 | 2768篇 |
国内免费 | 45篇 |
专业分类
耳鼻咽喉 | 314篇 |
儿科学 | 1058篇 |
妇产科学 | 720篇 |
基础医学 | 4428篇 |
口腔科学 | 866篇 |
临床医学 | 3993篇 |
内科学 | 5729篇 |
皮肤病学 | 432篇 |
神经病学 | 2891篇 |
特种医学 | 1128篇 |
外国民族医学 | 1篇 |
外科学 | 4987篇 |
综合类 | 639篇 |
一般理论 | 16篇 |
预防医学 | 3228篇 |
眼科学 | 1382篇 |
药学 | 2128篇 |
中国医学 | 14篇 |
肿瘤学 | 1876篇 |
出版年
2021年 | 478篇 |
2020年 | 309篇 |
2019年 | 511篇 |
2018年 | 622篇 |
2017年 | 447篇 |
2016年 | 455篇 |
2015年 | 537篇 |
2014年 | 858篇 |
2013年 | 1236篇 |
2012年 | 1687篇 |
2011年 | 1721篇 |
2010年 | 1012篇 |
2009年 | 860篇 |
2008年 | 1572篇 |
2007年 | 1670篇 |
2006年 | 1601篇 |
2005年 | 1668篇 |
2004年 | 1552篇 |
2003年 | 1406篇 |
2002年 | 1308篇 |
2001年 | 842篇 |
2000年 | 883篇 |
1999年 | 765篇 |
1998年 | 383篇 |
1997年 | 299篇 |
1996年 | 303篇 |
1995年 | 282篇 |
1994年 | 286篇 |
1993年 | 256篇 |
1992年 | 695篇 |
1991年 | 592篇 |
1990年 | 557篇 |
1989年 | 527篇 |
1988年 | 514篇 |
1987年 | 483篇 |
1986年 | 468篇 |
1985年 | 483篇 |
1984年 | 376篇 |
1983年 | 352篇 |
1982年 | 262篇 |
1981年 | 258篇 |
1980年 | 225篇 |
1979年 | 363篇 |
1978年 | 288篇 |
1977年 | 241篇 |
1976年 | 217篇 |
1974年 | 268篇 |
1973年 | 274篇 |
1972年 | 221篇 |
1971年 | 216篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Masha Y Ivanova Allen C Israel 《Journal of clinical child and adolescent psychology》2006,35(4):564-570
Family stability, defined as the consistency of family activities and routines, was examined in a sample of urban families (n = 70) with children (ages 7 to 16) receiving psychological services. Parent-reported family stability was associated with lower parent-reported children's internalizing behavior problems. Child-reported family stability significantly attenuated the influence of parental depressive symptoms on parent-reported children's internalizing, externalizing, and total behavior problems, while controlling for the effect of children's age. Parental depressive symptoms were associated with problems in child adjustment only at the low level of family stability. 相似文献
992.
Francisella tularensis (Ft) is a Gram-negative bacterium and the causative agent of tularemia. It is well established that this organism replicates inside macrophages, but we are only beginning to understand this interface at the molecular level. Herein, we compared directly the ability of Ft subspecies holarctica live-vaccine strain to infect freshly isolated human peripheral blood monocytes, monocyte-derived macrophages (MDM), and cells of the murine macrophage cell line J774A.1 (J774). We now show that unopsonized bacteria infected human MDM fivefold more efficiently than monocytes or J774 cells in standard media. Moreover, enhanced infection of MDM was mediated, in part, by the macrophage mannose receptor (MR). Forming Ft phagosomes accumulated MR, and infection was inhibited by MR-blocking antibody or soluble mannan but not by the dectin-1 ligand laminarin. Up-regulation of MR in MDM (by exposure to interleukin-4) increased Ft phagocytosis, as did expression of MR in J774 cells. Conversely, opsonized Ft were ingested readily by monocytes and MDM. Medium supplementation with 2.5% fresh autologous serum was sufficient to confer opsonophagocytosis and CD11b accumulated in the membrane at sites of Ft engulfment. Infection of monocytes by opsonized Ft was nearly ablated by complement receptor 3 (CR3) blockade. Conversely, MDM used MR and CD11b/CD18 to ingest opsonized organisms. Altogether, our data demonstrate differential infection of mononuclear phagocytes by Ft and define distinct roles for MR and CR3 in phagocytosis. 相似文献
993.
Grant AJ Sheppard M Deardon R Brown SP Foster G Bryant CE Maskell DJ Mastroeni P 《Immunology》2008,125(1):28-37
Growth of Salmonella enterica in mammalian tissues results from continuous spread of bacteria to new host cells. Our previous work indicated that infective S. enterica are liberated from host cells via stochastic necrotic burst independently of intracellular bacterial numbers. Here we report that liver phagocytes can undergo apoptotic caspase-3-mediated cell death in vivo, with apoptosis being a rare event, more prevalent in heavily infected cells. The density-dependent apoptotic cell death is likely to constitute an alternative mechanism of bacterial spread as part of a bet-hedging strategy, ensuring an ongoing protective intracellular environment in which some bacteria can grow and persist. 相似文献
994.
Webb DC Mahalingam S Cai Y Matthaei KI Donaldson DD Foster PS 《European journal of immunology》2003,33(12):3377-3385
The pathogenesis of human asthma and the development of key features of pulmonary allergy in mouse models has been critically linked to IL-13. Analyses of the receptor components employed by IL-13 have shown that delivery of this cytokine to the airways of naive IL-4Ralpha gene targeted (IL-4Ralpha(-/-)) mice fails to induce disease, suggesting that this membrane protein is critical for transducing IL-13-mediated responses. The current study demonstrates that, in contrast to naive mice, T helper 2 bias, airways hyperreactivity (AHR) and tissue eosinophilia develop in Ovalbumin-sensitized IL-4Ralpha(-/-) mice and that these responses can be inhibited by the IL-13 antagonist sIL-13Ralpha2Fc. Therefore, antigen stimulation induces an IL-13-regulated response that is independent of IL-4Ralpha. To determine the role of IL-5 and eosinophils in the development of disease in antigen-exposed IL-4Ralpha(-/-) mice, pulmonary allergy was examined in mice deficient in both factors. IL-4Ralpha/IL-5(-/-) mice were significantly defective in their ability to produce IL-13 and failed to develop AHR, suggesting that IL-5 indirectly regulates AHR in allergic IL-4Ralpha(-/-) mice by an IL-13-dependent mechanism. Collectively, these results demonstrate that IL-13-dependent processes regulating the development of AHR and T helper bias persist in the in the lungs of allergic IL-4Ralpha(-/-) mice. 相似文献
995.
Foster RR Slater SC Seckley J Kerjaschki D Bates DO Mathieson PW Satchell SC 《The American journal of pathology》2008,173(4):938-948
We have previously reported expression of vascular endothelial growth factor (VEGF)-A and -C in glomerular podocytes and actions of VEGF-A on glomerular endothelial cells (GEnC) that express VEGF receptor-2 (VEGFR-2). Here we define VEGFR-3 expression in GEnC and investigate the effects of the ligand VEGF-C. Renal cortex and cultured GEnC were examined by microscopy, and both cell and glomerular lysates were assessed by Western blotting. VEGF-C effects on trans-endothelial electrical resistance and albumin flux across GEnC monolayers were measured. The effects of VEGF-C156S, a VEGFR-3-specific agonist, and VEGF-A were also studied. VEGF-C effects on intracellular calcium ([Ca2+]i) were measured using a fluorescence technique, receptor phosphorylation was examined by immunoprecipitation assays, and phosphorylation of myosin light chain-2 and VE-cadherin was assessed by blotting with phospho-specific antibodies. GEnC expressed VEGFR-3 in tissue sections and culture, and VEGF-C increased trans-endothelial electrical resistance in a dose-dependent manner with a maximal effect at 120 minutes of 6.8 Ω whereas VEGF-C156S had no effect. VEGF-C reduced labeled albumin flux by 32.8%. VEGF-C and VEGF-A increased [Ca2+]i by 15% and 39%, respectively. VEGF-C phosphorylated VEGFR-2 but not VEGFR-3, myosin light chain-2, or VE-cadherin. VEGF-C increased GEnC monolayer integrity and increased [Ca2+]i, which may be related to VEGF-C-S particular receptor binding and phosphorylation induction characteristics. These observations suggest that podocytes direct GEnC behavior through both VEGF-C and VEGF-A. 相似文献
996.
Wang S Baer L Kunselman AR Myers JL Undar A 《ASAIO journal (American Society for Artificial Internal Organs : 1992)》2008,54(4):416-422
This study investigated delivery of gaseous microemboli (GME) with vacuum-assisted venous drainage (VAVD) at various flow rates and perfusion modes in a simulated neonatal cardiopulmonary bypass (CPB) model. Four transducers (postpump, postoxygenator, postfilter, and venous line) of the emboli detection and classification (EDAC) quantifier were inserted into the CPB circuit to detect and classify GME. Four negative pressures (0, -15, -30, and -45 mm Hg), 3 flow rates (750, 1,000, and 1,250 ml/min), and 2 perfusion modes (pulsatile and nonpulsatile) were tested. After injecting 10 ml air into the venous line via an 18G needle, 2-minute segments of data were recorded simultaneously through 4 transducers. This entire process was repeated 6 times for each unique combination of pressure, flow rate, and perfusion mode, yielding a total of 144 experiments. Independent of perfusion mode and flow rate, the use of VAVD with higher negative pressures delivered significantly more GME at the postpump site. There was no difference in delivery at the postfilter site. The majority of GME were trapped by the Capiox Baby-RX hollow-fiber membrane oxygenator. Compared with nonpulsatile flow, pulsatile flow transferred more GME at the postpump site at all 3 flow rates. Our results suggest that VAVD with higher negative pressures, increased flow rates, and pulsatile flow could deliver more GME at the postpump site when a fixed volume air is introduced into the venous line. The Emboli Detection and Classification Quantifier is a sensitive tool for the detection and classification of GME as small as 10 microns in this simulated neonatal model. 相似文献
997.
OBJECTIVE: Breast arterial calcifications (BACs) are common but unreported findings on screening mammograms. This study correlated mammographically detected BACs with coronary artery disease (CAD) risk factors and a history of atherosclerotic cardiovascular disease (ASCVD), estimating the relative risk of ASCVD in patients with BACs. DESIGN: Women arriving for breast cancer screening mammography gave their consent to complete a questionnaire and to allow their mammograms to be analyzed independently for the presence of BACs by certified radiologists, who were blinded to the results of the questionnaire. The questionnaire assessed major risk factors for CAD and gathered information on hormone therapy use. RESULTS: Of the 1,919 women with results, 268 were BAC positive, giving a BAC prevalence of 14%. Five cardiovascular risk factors (age, hypertension, hypercholesteremia, diabetes mellitus, and menopause) were significantly more prevalent in the BAC-positive population (P < 0.001). The BAC-positive group also had a significantly higher (P < 0.001) occurrence of ASCVD events (angina, previous myocardial infarction, previous abnormal angiography, previous stroke, and previous coronary artery bypass graft). Multiple logistic regression analysis found BACs to be strongly associated with ASCVD events (odds ratio = 2.29, 95% CI: 1.40-3.74) as compared with other CAD risk factors (including hypertension, cigarette smoking, diabetes mellitus, age, and family history of ASCVD). The association of BAC with ASCVD was present even after accounting for age. CONCLUSIONS: BACs are associated with an increased prevalence of both cardiovascular risk factors and cardiovascular morbidity. BACs may be a practical tool to use as a risk indicator for CAD in women. 相似文献
998.
We determined the complete nucleotide sequence of the Rose spring dwarf-associated virus (RSDaV) genomic RNA (GenBank accession no. EU024678) and compared its predicted RNA structural characteristics affecting gene expression. A cDNA library was derived from RSDaV double-stranded RNAs (dsRNAs) purified from infected tissue. Nucleotide sequence analysis of the cloned cDNAs, plus for clones generated by 5'- and 3'-RACE showed the RSDaV genomic RNA to be 5808 nucleotides. The genomic RNA contains five major open reading frames (ORFs), and three small ORFs in the 3'-terminal 800 nucleotides, typical for viruses of genus Luteovirus in the family Luteoviridae. Northern blot hybridization analysis revealed the genomic RNA and two prominent subgenomic RNAs of approximately 3 kb and 1 kb. Putative 5' ends of the sgRNAs were predicted by identification of conserved sequences and secondary structures which resembled the Barley yellow dwarf virus (BYDV) genomic RNA 5' end and subgenomic RNA promoter sequences. Secondary structures of the BYDV-like ribosomal frameshift elements and cap-independent translation elements, including long-distance base pairing spanning four kb were identified. These contain similarities but also informative differences with the BYDV structures, including a strikingly different structure predicted for the 3' cap-independent translation element. These analyses of the RSDaV genomic RNA show more complexity for the RNA structural elements for members of the Luteoviridae. 相似文献
999.
Hou Y Matthews AR Smitherman AM Bulick AS Hahn MS Hou H Han A Grunlan MA 《Biomaterials》2008,29(22):3175-3184
Poly(N-isopropylacrylamide) (PNIPAAm) hydrogels become more hydrophobic when they reversibly switch from a water-swollen to a deswollen state above the volume phase transition temperature (VPTT, approximately 33 degrees C) which has been used to modulate cell adhesion. In the current work, we prepared novel thermoresponsive nanocomposite hydrogels comprised of a PNIPAAm hydrogel matrix and polysiloxane colloidal nanoparticles ( approximately 220 nm average diameter) via in situ photopolymerization of aqueous solutions of NIPAAm monomer, N,N'-methylenebisacrylamide (BIS, crosslinker), photoinitiator and polysiloxane nanoparticles (0.5-2.0 wt% based on solution weight) at approximately 7 degrees C. The VPTT of the nanocomposite hydrogels is not altered versus the pure PNIPAAm hydrogel. Dynamic mechanical analysis and tensile tests revealed that higher nanoparticle content generally produced improved hydrogel mechanical properties. Surfaces of nanocomposite hydrogels became increasingly more hydrophobic at all temperatures between 10 and 40 degrees C as the amount of hydrophobic polysiloxane nanoparticles was increased. When cooled from 37 to 25 degrees C, mouse smooth muscle precursor cells (10T1/2) were effectively detached from nanocomposite hydrogel surfaces. The utility of photopatterning to create surface micropillars comprised of nanocomposite hydrogels was demonstrated. 相似文献
1000.