全文获取类型
收费全文 | 119957篇 |
免费 | 7251篇 |
国内免费 | 1589篇 |
专业分类
耳鼻咽喉 | 1593篇 |
儿科学 | 2995篇 |
妇产科学 | 4113篇 |
基础医学 | 18439篇 |
口腔科学 | 3616篇 |
临床医学 | 9391篇 |
内科学 | 21983篇 |
皮肤病学 | 2469篇 |
神经病学 | 8057篇 |
特种医学 | 4065篇 |
外国民族医学 | 3篇 |
外科学 | 16994篇 |
综合类 | 5240篇 |
一般理论 | 35篇 |
预防医学 | 8726篇 |
眼科学 | 2842篇 |
药学 | 10301篇 |
中国医学 | 832篇 |
肿瘤学 | 7103篇 |
出版年
2021年 | 1035篇 |
2019年 | 1103篇 |
2018年 | 1665篇 |
2017年 | 1201篇 |
2016年 | 1235篇 |
2015年 | 1483篇 |
2014年 | 1938篇 |
2013年 | 2505篇 |
2012年 | 3652篇 |
2011年 | 3931篇 |
2010年 | 2326篇 |
2009年 | 2098篇 |
2008年 | 3462篇 |
2007年 | 3688篇 |
2006年 | 3677篇 |
2005年 | 3240篇 |
2004年 | 3025篇 |
2003年 | 2816篇 |
2002年 | 2664篇 |
2001年 | 6757篇 |
2000年 | 6954篇 |
1999年 | 5727篇 |
1998年 | 1838篇 |
1997年 | 1388篇 |
1996年 | 940篇 |
1995年 | 867篇 |
1992年 | 3748篇 |
1991年 | 3822篇 |
1990年 | 3557篇 |
1989年 | 3563篇 |
1988年 | 3437篇 |
1987年 | 3299篇 |
1986年 | 3098篇 |
1985年 | 2980篇 |
1984年 | 2054篇 |
1983年 | 1792篇 |
1982年 | 987篇 |
1979年 | 1912篇 |
1978年 | 1184篇 |
1977年 | 988篇 |
1976年 | 920篇 |
1975年 | 1191篇 |
1974年 | 1361篇 |
1973年 | 1414篇 |
1972年 | 1357篇 |
1971年 | 1247篇 |
1970年 | 1137篇 |
1969年 | 1121篇 |
1968年 | 1024篇 |
1967年 | 897篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
991.
Abstract We previously demonstrated that epidermal growth factor (EGF) induces a several-fold increase in ornithine decarboxylase (ODC) activity and the steady-state level of ODC mRNA in cultured SV40-transformed human keratinocytes (1). Pretreatment of cell cultures with ultraviolet B (UVB) radiation resulted in a reduction of EGF-induced ODC activity. To determine whether UVB inhibits the accumulation of ODC mRNA by EGF, cells were pretreated with 20 mJ/cm2 UVB or sham-irradiated and then incubated with 100 ng/ml EGF. Northern blot analysis revealed that UVB irradiation entirely blocked the EGF induction of ODC mRNA. Since the binding of EGF to its plasma membrane receptor is the first step in initiating a biological response, the effect of UVB on EGF binding was evaluated. UVB treatment of cultured keratinocytes resulted in an immediate and dose-dependent reduction of EGF binding. Scatchard analysis revealed thai the reduction of EGF binding was due to a 52% decrease in the number of available receptors, from 6.2 × 104/cell to 3.0 × 104/cell. However, UVB decreased the EGF-binding affinity very little (Kd = 0.60 nM in control and Kd=0.75 nM in UVB-treated Z114 cells). In addition, UVB did not alter the rate of EGF internalization. These data suggest that UVB blocks the signal transduction pathway of EGF that is involved in regulation of ODC gene expression. Immunoblot analysis of extracts from irradiated cells showed that UVB induced tyro-sine phosphorylation of EGFR and that the quantity of EGFR protein was unaffected by UVB treatment. Phosphorylation of EGFR may be responsible for decreased binding of EGF to its receptor. 相似文献
992.
Over the past decade, research on medications to treat alcohol problem has flourished. Naltrexone and acamprosate are tangible
fruits of such endeavors and each has now earned approval in a large number of countries. Recent studies on naltrexone indicate
that patient compliance is important if full benefits are to be achieved. Several laboratory studies with human subjects are
beginning to elucidate the mechanisms underlying efficacy of naltrexone, as well as explaining variability of response among
subpopulations of drinkers. In addition to these two agents, recent investigations have also demonstrated that the antidepressants
desipramine, imipramine, and fluoxetine reduce mood-related symptoms and, to some extent, drinking itself in alcoholics who
are depressed. Research to date suggests that opioid antagonists and selective serotonin reuptake inhibitors are more effective
in reducing alcohol intake when used in combination. Clinical issues, methodology, and directions for future research are
also reviewed in this article. In particular, issues addressed include alternative dosage regimens, necessary duration of
treatment, employment of medications in combination, integration of pharmacologic agents with behavioral interventions, enhancement
of patient compliance, and concurrent treatment of psychiatric comorbidity.
Received: 16 December 1997 / Final version: 15 April 1998 相似文献
993.
Z J He K Nakayama 《Proceedings of the National Academy of Sciences of the United States of America》1995,92(24):11155-11159
Although attention plays a significant role in vision, its spatial deployment and spread in the third dimension is not well understood. In visual search experiments we show that we cannot easily focus attention across isodepth loci unless they are part of a well-formed surface with locally coplanar elements. Yet we can easily spread our attention selectively across well-formed surfaces that span an extreme range of stereoscopic depths. In cueing experiments, we show that this spread of attention is, in part, obligatory. Attentional selectivity is reduced when targets and distractors are coplanar with or rest on a common receding stereoscopic plane. We conclude that attention cannot be efficiently allocated to arbitrary depths and extents in space but is linked to and spreads automatically across perceived surfaces. 相似文献
994.
High density plating procedure was used to evaluate the effect of atrazine on anterior pituitary cells of rats in monolayer culture. Collagenase-dispersed pituitary cells plated in suspension with medium-199 and 10% foetal calf serum attached quantitatively to plastic surfaces within 24 hours. Electron microscopy showed subpopulations of different cell types. After prolonged cultivation, most cells established small colonies with extensive contacts among them. Cell-to-cell formation of aggregates was significant and the colonies manifested morphological changes. The cells retained their enzymatic activity, converting testosterone into 5 alpha-dihydrotestosterone by enzyme 5 alpha-reductase. Immunohistochemical techniques facilitated differentiation of gonadotrophs producing follicle stimulating hormone (FSH) and luteinising hormone (LH). Atrazine in concentrations of 5 to 50 micrograms/ml of medium was associated with a significant reduction in the number of viable cells within 72 hours. The results suggest that the pituitary cell culture may prove useful in toxicological testing of various toxic compounds and reduce or replace in vivo animal experiments. 相似文献
995.
Cytokines and adhesion molecules in renal vasculitis and lupus nephritis 总被引:20,自引:1,他引:19
Tesar V; Masek Z; Rychlik I; Merta M; Bartunkova J; Stejskalova A; Zabka J; Janatkova I; Fucikova T; Dostal C; Becvar R 《Nephrology, dialysis, transplantation》1998,13(7):1662-1667
Background: Plasma levels of some pro-inflammatory
cytokines and soluble adhesion molecules have been suggested to be useful
parameters to assess the activity of antineutrophil cytoplasmic antibody
(ANCA)-positive vasculitis and lupus nephritis. We hypothesized that the
renal activity of these diseases is better reflected by the urinary
excretion and fractional excretion of these molecules.
Methods: Plasma levels and urinary excretion of tumour
necrosis factor-&agr; (TNF-&agr;), interleukin (IL)-6, IL-8, and
the soluble cell adhesion molecules sICAM-1 and sVCAM-1 were measured by
enzyme-linked immunosorbent assay (ELISA) in 15 patients with ANCA-positive
renal vasculitis (eight active, ANCA-A; six in remission, ANCA-R), six
patients with active lupus nephritis (LN), 15 patients with IgA nephropathy
(IgAN) and nine healthy subjects. Fractional excretion of selected
cytokines and adhesion molecules was also calculated.
Results: Patients with ANCA-A had increased urinary
excretion and fractional excretion of TNF-&agr; (9.27±3.19%
vs 0.58±0.02%, P<0.01), IL-6
(120.79±65.83% vs 1.89±0.34%,
P<0.01) and increased fractional excretion of IL-8
(23.34±6.38% vs 2.56±1.07%,
P<0.01) and sVCAM-1 (0.81±0.33% vs
0.03±0.02%, P<0.01) compared with controls. Urinary
excretion of TNF-&agr; and IL-6 and fractional excretion of
TNF-&agr;, IL-6 and IL-8 were higher in ANCA-A than in ANCA-R. Patients
with LN had increased plasma TNF-&agr; (20.52±2.01 pg/ml
vs 12.33±0.23 pg/ml, P<0.05) and
sVCAM-1 (1537.88±276.36 ng/ml vs
692.26±44.42 ng/ml, P<0.05) and increased urinary
excretion of TNF-&agr; (2.81±0.51 &mgr;g/mol creat
vs 0.98±0.05 &mgr;g/mol creat,
P<0.01), IL-8 (35.78±14.03 &mgr;g/mol creat
vs 12.46±5.19 &mgr;g/mol creat,
P<0.05) and sVCAM-1 (48.98±20.20 &mgr;g/mol creat
vs 2.92±1.35 &mgr;g/mol creat,
P<0.01) compared with controls. Patients with IgAN had, in
comparison with controls only increased plasma TNF-&agr;
(18.10±0.57 pg/ml vs 12.33±0.23
pg/ml, P<0.05). Conclusions: Urinary excretion
and fractional excretion, but not plasma levels of selected proinflammatory
cytokines (TNF-&agr;, IL-6 and IL-8) were increased in patients with
active ANCA-positive renal vasculitis, but not in ANCA positive vasculitis
in remission. These parameters may be useful to monitor the activity of
this disease. 相似文献
996.
997.
998.
C Z Hong F Batkin J Yu E B San Luis 《Archives of physical medicine and rehabilitation》1988,69(9):685-688
Axillary F-loop latencies (AFLL) were measured on median and ulnar nerves of 54 normal volunteers. The median and ulnar nerves were stimulated at the wrist and at the axilla 25cm distal to the sternal notch. The compound muscle action potentials were recorded from thenar and hypothenar muscles. Averaged tracings from 32 consecutive stimuli at the wrist were obtained. The averaged F-wave latencies were measured to the peak (Fwp) of the averaged F-wave. The M-wave latencies from wrist and axilla stimulation were measured to the onset of the wave (Mw and Ma, respectively). The averaged AFLL (a-AFLL) was calculated as (Fwp + Mw)-2 Ma. The average values of a-AFLL were 14.12 +/- 0.88msec for median nerve, and 13.97 +/- 0.90msec for ulnar nerve. There was no significant difference between male and female subjects, nor between the right and left sides. Seven subjects with EMG evidence of C8 or C8 to T1 radiculopathy, although manifesting normal AFLL gauged by the regular method (ie, measured to the onset of the shortest F-wave latency among eight tracings), had significantly longer "averaged AFLL" in both median and ulnar nerves of the affected side than the a-AFLL obtained from the normal side. It is concluded that the a-AFLL is a more sensitive measure than the "regular AFLL" in the assessment of proximal nerve lesion (especially C8 or C8 to T1 radiculopathy). 相似文献
999.
Alcohollike liver disease in nonalcoholics. A clinical and histologic comparison with alcohol-induced liver injury 总被引:29,自引:0,他引:29
Individuals who deny alcohol consumption may develop liver injury that histologically resembles the liver injury found in alcoholic patients. To determine whether any clinical or histologic features distinguish alcoholic and nonalcoholic subjects with "alcohollike" liver injury, the clinical records and liver biopsy specimens of 68 alcoholic and 39 nonalcoholic patients with alcohollike injury on liver biopsy were compared. The clinical and biochemical features of the two groups differed significantly. Alcoholism was associated with more severe clinical and biochemical manifestations of liver disease. However, there was considerable overlap among histologic features of the two clinically defined groups. Based on histology alone, alcoholic and nonalcoholic patients were often indistinguishable. The observations suggest that the clinical differences between the alcoholic and non-alcoholic patients cannot be attributed to qualitative or quantitative differences in liver histology. On the other hand, histologic similarities between the two groups raise the possibility that a shared condition, perhaps nutritional or hormonal, is responsible for the histologic expression of alcohollike injury in both groups. 相似文献
1000.
Patterns of calcifications and cholangiographic findings in hepatobiliary tuberculosis 总被引:3,自引:0,他引:3
Dean D. T. Maglinte M.D. Sol Z. Alvarez Anastacio C. Ng Jose L. Lapeña 《Abdominal imaging》1988,13(1):331-335
The radiologic findings on conventional examinations (plain films and cholangiograms) in a large group of patients with proven hepatobiliary tuberculosis are reviewed. The plain film findings of large chalky and confluent hepatic calcifications or nodal-type calcifications along the course of the common bile duct are suggestive of hepatobiliary tuberculosis. Small, discrete, scattered calcifications may be mimicked by histoplasmosis but can be differentiated from hepatobiliary tuberculosis. Obstructing defects seen on cholangiography are indicative of tuberculosis when adjacent calcifications are present. The patterns of liver calcifications could provide a clue to the diagnosis of hepatobiliary tuberculosis and its differentiation from liver calcifications of various other etiologies. 相似文献