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   1364973篇
  免费   103867篇
  国内免费   4295篇
耳鼻咽喉   17123篇
儿科学   44543篇
妇产科学   37015篇
基础医学   202790篇
口腔科学   36141篇
临床医学   132459篇
内科学   265453篇
皮肤病学   27012篇
神经病学   114868篇
特种医学   49114篇
外国民族医学   390篇
外科学   188112篇
综合类   28833篇
现状与发展   1篇
一般理论   465篇
预防医学   116506篇
眼科学   29518篇
药学   100992篇
  6篇
中国医学   3230篇
肿瘤学   78564篇
  2021年   11352篇
  2019年   12128篇
  2018年   17239篇
  2017年   12940篇
  2016年   13897篇
  2015年   16006篇
  2014年   21623篇
  2013年   33337篇
  2012年   46557篇
  2011年   49150篇
  2010年   28153篇
  2009年   25771篇
  2008年   44769篇
  2007年   47173篇
  2006年   47152篇
  2005年   45666篇
  2004年   43570篇
  2003年   41348篇
  2002年   40079篇
  2001年   61612篇
  2000年   63319篇
  1999年   52927篇
  1998年   14726篇
  1997年   13377篇
  1996年   13222篇
  1995年   12550篇
  1994年   11719篇
  1993年   10992篇
  1992年   41978篇
  1991年   41109篇
  1990年   39793篇
  1989年   37686篇
  1988年   34884篇
  1987年   34003篇
  1986年   32403篇
  1985年   30889篇
  1984年   23223篇
  1983年   19729篇
  1982年   11842篇
  1979年   20928篇
  1978年   14893篇
  1977年   12143篇
  1976年   11944篇
  1975年   12174篇
  1974年   14899篇
  1973年   14554篇
  1972年   13445篇
  1971年   12511篇
  1970年   11570篇
  1969年   10511篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The aim of the present study was to present data from dental care habits and knowledge of oral health in two cross-sectional studies carried out in 1973 and 1983. A random sample of approximately 1000 individuals evenly distributed in the age groups 3, 5, 10, 15, 20, 30, 40, 50, 60 and 70 years was studied for each of these two years. In the 1983-year examination 80 individuals 80 years of age were also included. All subjects were inhabitants of the community of J?nk?ping, Sweden. A questionnaire about dental care habits and knowledge was used in combination with a clinical and radiographical examination. The participants answered 23-101 questions. The same questions were raised in 1973 and 1983. For most age groups more then 80 per cent visited a dentist yearly in 1983. This yearly attendance was higher than that for 1973. In the 20-year-old group 14 per cent of the individuals received dental care in the PDS in 1973 compared to 63 per cent in 1983. The main reason to visit a dentist in 1973 was by the patient's own initiative while in 1983 the appointments were based on the dentist's initiative. The number of subjects that felt discomfort in connection with a visit to the dentist had decreased between 1973 and 1983. Knowledge about the etiology of caries had increased between 1973 and 1983 was not the case for gingivitis and periodontitis. An increase had occurred in toothbrushing frequency and the use of toothpicks and disclosing tablets but this between 1973 and 1983. In 1983, 98 to 93 per cent of the subjects in the age groups 10-30 years had been exposed to topical fluorides. The corresponding figure for 30-year-olds in 1973 was 1 per cent. It is obvious that during the period 1973 to 1983 there has been an increase in dental attendance, knowledge of dental diseases, oral health and the use of preventive measures.  相似文献   
992.
The effects of aging on diencephalic (A-11, A-12, A-13, A-14) catecholamine neurons in the F344 male rat were examined with Falck-Hill?rp histofluorescence. In contrast to the age-related increase in A-12 perikaryal fluorescence intensity previously reported (Hoffman and Sladek: Neurobiol. Aging 1:27-37, '80), incertohypothalamic perikarya showed decreased (A-13) or unchanged (A-11, A-14) fluorescence intensity with age. Cell counts of fluorescent A-12 perikarya disclosed a 47% increase in the number of fluorescent A-12 neurons in 30-month-old F344 rats relative to the 3-month-old controls; numbers of A-11 and A-13 fluorescent perikarya decreased with age, but the declines were not statistically significant. It is unlikely that the age-related increase in number of fluorescent A-12 perikarya is the result of proliferation of neurons in the aged F344 rat. Rather, the greater number of fluorescent A-12 perikarya in 30-month-old F344 rats indicates that some A-12 neurons in 3-month-old F344 rats contain levels of dopamine that are subthreshold for detection with the Falck-Hill?rp fluorescence technique, whereas virtually all A-12 perikarya in 30-month-old F344 rats contain detectable quantities of dopamine. These findings suggest that diencephalic catecholamine neurons exhibit divergent changes in transmitter content and cell number that may reflect varying degrees of functional integrity during brain aging.  相似文献   
993.
Two experiments were carried out in order to separate the effects of the behavioral and the anatomical components of female sexual attractiveness in baboons. In the first experiment, two ovariectomized females were given increasing dosages of exogenous estradiol benzoate, and data were collected on their behavior as well as on male sexual arousal as assessed by the occurrence of coagulated seminal emissions of the type that result from masturbation. Male sexual arousal levels increased positively with the females' perineal swellings and appeared relatively unrelated to the females' behavior. In the second experiment, data were collected from five different groups of males in a systematic fashion across the period of a full menstrual cycle for their varied stimulus female partners. Behavior observations were carried out on the five different stimulus females, and ratings also were made of fluctuations in their perineal tumescence. The results of this experiment make it clear that male sexual arousal fluctuated across the study cycles in a fashion very similar to that of the perineal swellings of the stimulus females. Behavior was shown during all phases of the cycle, and, although it may have had a positive influence on male arousal during the follicular phase of the female's cycle, it had no apparent effect during the luteal phase. These results taken together establish for the first time that an estrogen stimulated female perineum per se has the potential to sexually arouse the male baboon. In addition, the data suggest that, although behavior may exert a positive effect on male arousal, in the absence of an estrogen stimulated perineum it is not sufficient to arouse males to masturbate. Finally the results establish that, although intact females appear to show behavior increases which may be arousing to males around the time of ovulation, these behaviors do not have to be shown by a female in order to arouse a male, provided she is swollen.  相似文献   
994.
Absence of antibody production in patients treated with botulinum A toxin   总被引:4,自引:0,他引:4  
To test the possibility of the formation of an antibody to botulinum A toxin after multiple injections of this potent neurotoxin, we collected serum samples from 28 patients who received 57 doses. These injections over a nine-month period with as much as 50 units per injection formed no detectable antibody.  相似文献   
995.
996.
997.
Arsenic pollution has become increasingly severe. It occurs as the result of geological processes and different human activities. Arsenic toxicity at the respiratory level occurs mainly by inhalation of products of coal combustion. The aim of this study was to evaluate sodium arsenite (As3+) toxicity in murine alveolar macrophages (AMs) in vitro and its association with the alterations in cell metabolism.

No changes in viability, apoptosis or cell area were detected in AMs treated with As3+ concentrations up to 2 μM for 24–96 h. A marked decrease in these end-points was observed for As3+ concentrations ranging from 2.5 μM to 10 μM.

Regarding the dynamics of the endo-exocytic process triggered by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell incorporation, no variations were detected for As3+ concentrations lower than 2 μM while higher concentrations markedly modified this response.

MTT specific activity, as a measure of cell metabolic activity, was not modified irrespective of the As3+ concentration assayed. However, nitroblue tetrazolium (NBT) specific activity, as a measure of superoxide anion generation, is responsive but only to low As3+ doses.

Although this study focuses on lung macrophages, the effects of As3+ described herein may also apply to the response of macrophages residing in other organs.

Arsenite modifies the metabolic and the oxidative status of AMs in vitro. When macrophages are in an As3+ rich medium, they exhibit a reduction in respiratory burst levels and lose their intrinsic capacity to respond to toxicants.  相似文献   

998.
PURPOSE: The aim of this study was to verify hyperthermia treatment planning calculations by means of measurements performed during hyperthermia treatments. The calculated specific absorption rate (SAR(calc)) was compared with clinically measured SAR values, during 11 treatments in seven cervical carcinoma patients. METHODS: Hyperthermia treatments were performed using the 70 MHz AMC-4 waveguide system. Temperatures were measured using multisensor thermocouple probes. One invasive thermometry catheter in the cervical tumour and two non-invasive catheters in the vagina were used. For optimal tissue contact and fixation of the catheters, a gynaecological tampon was inserted, moisturized with distilled water (4 treatments), or saline (6 treatments) for better thermal contact. During one treatment no tampon was used. At the start of treatment the temperature rise (DeltaT(meas)) after a short power pulse was measured, which is proportional to SAR(meas). The SAR(calc) along the catheter tracks was extracted from the calculated SAR distribution and compared with the DeltaT(meas)-profiles. RESULTS: The correlation between DeltaT(meas) and SAR(calc) was on average R = 0.56 +/- 0.28, but appeared highly dependent on the wetness of the tampon (preferably with saline) and the tissue contact of the catheters. Correlations were strong (R approximately 0.85-0.93) when thermal contact was good, but much weaker (R approximately 0.14-0.48) for cases with poor thermal contact. CONCLUSION: Good correlations between measurements and calculations were found when tissue contact of the catheters was good. The main difficulties for accurate verification were of clinical nature, arising from improper use of the gynaecological tampon. Poor thermal contact between thermocouples and tissue caused measurement artefacts that were difficult to correlate with calculations.  相似文献   
999.
The bed nucleus of the stria terminalis (BNST) and its adrenergic input are key components in stress-induced reinstatement and maintenance of drug use. Intra-BNST injections of either beta-adrenergic receptor (beta-AR) antagonists or alpha2-adrenergic receptor (alpha2-AR) agonists can inhibit footshock-induced reinstatement and maintenance of cocaine- and morphine-seeking. Using electrophysiological recording methods in an in vitro slice preparation from C57/Bl6j adult male mouse BNST, we have examined the effects of adrenergic receptor activation on excitatory synaptic transmission in the lateral dorsal supracommissural BNST (dBNST) and subcommissural BNST (vBNST). Alpha2-AR activation via UK-14,304 (10 microM) results in a decrease in excitatory transmission in both dBNST and vBNST, an effect predominantly dependent upon the alpha2A-AR subtype. Beta-AR activation via isoproterenol (1 microM) results in an increase in excitatory transmission in dBNST, but not in vBNST. Consistent with the work with receptor subtype specific agonists, application of the endogenous ligand norepinephrine (NE, 100 microM) elicits two distinct effects on glutamatergic transmission. In dBNST, NE elicits an increase in transmission (62% of dBNST NE experiments) or a decrease in transmission (38% of dBNST NE experiments). In vBNST, NE elicits a decrease in transmission in 100% of the experiments. In dBNST, the NE-induced increase in synaptic transmission is blocked by beta1/beta2- and beta2-, but not beta1-specific antagonists. In addition, this increase is also reduced by the alpha2-AR antagonist yohimbine and is absent in the alpha2A-AR knockout mouse. In vBNST, the NE-induced decrease in synaptic transmission is markedly reduced in the alpha2A-AR knockout mouse. Further experiments demonstrate that the actions of NE on glutamatergic transmission can be correlated with beta-AR function.  相似文献   
1000.
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