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   71200篇
  免费   5029篇
  国内免费   183篇
耳鼻咽喉   1035篇
儿科学   1903篇
妇产科学   1669篇
基础医学   11627篇
口腔科学   1842篇
临床医学   6526篇
内科学   14149篇
皮肤病学   1017篇
神经病学   6440篇
特种医学   2895篇
外国民族医学   46篇
外科学   9740篇
综合类   593篇
一般理论   89篇
预防医学   5465篇
眼科学   1918篇
药学   4917篇
中国医学   167篇
肿瘤学   4374篇
  2022年   618篇
  2021年   1275篇
  2020年   800篇
  2019年   1157篇
  2018年   1358篇
  2017年   957篇
  2016年   1115篇
  2015年   1272篇
  2014年   1625篇
  2013年   2648篇
  2012年   3470篇
  2011年   3523篇
  2010年   2506篇
  2009年   2109篇
  2008年   3193篇
  2007年   3338篇
  2006年   3271篇
  2005年   3121篇
  2004年   3143篇
  2003年   2871篇
  2002年   2955篇
  2001年   2313篇
  2000年   2355篇
  1999年   2109篇
  1998年   948篇
  1997年   779篇
  1996年   696篇
  1995年   721篇
  1994年   601篇
  1993年   636篇
  1992年   1518篇
  1991年   1463篇
  1990年   1394篇
  1989年   1371篇
  1988年   1160篇
  1987年   1152篇
  1986年   1092篇
  1985年   1009篇
  1984年   721篇
  1983年   674篇
  1982年   473篇
  1981年   460篇
  1980年   390篇
  1979年   653篇
  1978年   392篇
  1977年   371篇
  1975年   388篇
  1974年   432篇
  1973年   363篇
  1972年   354篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Rasmussen and Milner [N.Y. Acad. Sci. Vol. 299, pp. 355–379, 1977] published data on late-lesioned (after age 6) epileptic patients who had suffered left hemisphere lesions. They estimated that left hemisphere dominance occurred in 96% of dextrals and 70% of sinistrals. These figures have been regarded as valid estimates for normal dextrals and sinistrals. We administered the Bilateral Object Naming Latency Task, a verbal tachistoscopic task with very good psychometric properties, to 188 dextral and 72 sinistral normals. Results showed that 93.6% of the dextrals and 80.3% of the sinistrals were left hemisphere dominant. A consideration of results from a number of carefully conducted dichotic listening studies suggests, as do present results, that the 70% left-dominance estimate of Rasmussen and Milner for normal sinistrals may be too low by about 10%. It is suggested that ‘bilateral dominance’, present in 15% of the epileptic sinistrals of Rasmussen and Milner, may be much less common in normal sinistrals.  相似文献   
82.
Previous studies of human thyroid cells in culture (mostly from pathological tissues) failed to demonstrate a mitogenic effect of TSH, leading to the proposal that the growth effect of TSH in vivo might be indirect. To reexamine the influence of TSH on DNA synthesis and cell proliferation, we established primary cultures of normal thyroid tissue from nine subjects. When seeded in a 1% serum-supplemented medium, thyroid follicles released by collagenase/dispase digestion developed as a cell monolayer that responded to TSH by rounding up and by cytoplasmic retraction. When seeded in serum-free medium, the cells remained associated in dense aggregates surrounded by few slowly spreading cells. In the latter condition, the cells responded to TSH and other stimulators of cAMP production, such as cholera toxin and forskolin, by displaying very high iodide-trapping levels. Exposure to serum irreversibly abolished this differentiated function. TSH stimulated the proliferation (as shown by DNA content per culture dish) of 1% serum cultured cells (doubling times were reduced from 106 to 76 h) and increased by 100% the [3H]thymidine labeling indices. In serum-free cultured cells (dense aggregates or cell monolayers after initial seeding with serum), control levels of DNA synthesis were lower, and up to 8-fold stimulation of DNA synthesis occurred in response to 100 mU/L TSH (stimulation was consistently detected with 20 mU/L), based on measurements of [3H]thymidine incorporation into acid-precipitable material and counts of labeled nuclei on autoradiographs (up to 40% labeled nuclei within 24 h). The mitogenic effect of TSH required a high insulin concentration (8.3 X 10(-7) mol/L) or a low insulin-like growth factor I concentration. The mitogenic effects of TSH were mimicked in part by cholera toxin, forskolin, and dibutyryl cAMP. Epidermal growth factor and phorbol myristate ester also stimulated thyroid cell proliferation and DNA synthesis, but they potently inhibited TSH-stimulated iodide transport. We conclude that TSH, acting at least in part through cAMP, is a potent growth factor for human thyroid cells and thus provide an experimental basis in vitro for the well established in vivo goitrogenic action of TSH.  相似文献   
83.
In a follow-up evaluation of 3721 Multiload IUD users, the removal rate for medical reasons other than bleeding/pain was only 2.6 per 100 women at three years. Most of these removals were for reasons that appeared to be unrelated to IUD use. The removal rate for pelvic inflammatory disease was 0.3 per 100 woman years. Women were followed up for up to three years after removal of their IUDs. Among women with PID at least 70% of those who desired pregnancy subsequently became pregnant, a rate similar to that of women who had their IUDs electively removed to become pregnant. The study provides further data on the safety of intrauterine contraception.
Resumen Durante el seguimiento de 3721 usuarias del DIU Multiload, la tasa de remociones por otras razones médicas que sangrado/dolor, fué de 2.6 por 100 mujeres en tres años. La mayoría de estas remociones fueron hechas por razones que parecen no estar relacionadas con el uso del DIU. La tasa de remociones por enfermedad inflamatoria pelviana fué de 0.3 por 100 años-mujer. Las mujeres tuvieron seguimiento hasta tres años después de la remoción de sus DIU. Entre las mujeres con enfermedad inflamatoria pelviana, al menos 70% de las que desearon un embarazo lo consiguieron; una tasa similar a la de mujeres que eligieron la remoción del DIU para quedar embarazadas. El estudio proporciona más información sobre la inocuidad de la anticoncepción intrauterina.

Résumé Lors d'une évaluation de suivi effectuée sur 3721 utilisatrices de DIU Multiload, le taux de retrait pour des raisons médicales autres que des pertes sanguines/douleurs n'a atteint que 2,6 pour cent des femmes après trois ans. La plupart de ces retraits ont été pratiqués pour des raisons qui ne semblaient pas liées à l'utilisation du DIU. Le taux de retrait pour cause d'inflammation pelvienne s'est élevé à 0,3 pour cent femmes-an. Les femmes ont été suivies pendant des périodes allant jusqu'à trois ans après le retrait du DIU. Parmi les patientes qui avaient contracté une inflammation pelvienne, 70% au moins de celles qui souhaitaient une grossesse sont par la suite devenues enceintes; taux semblable à celui des femmes qui avaient choisi de ne plus porter leur DIU précisément pour avoir un enfant. Cette étude fournit des données supplémentaires sur la sécurité qu'apporte la contraception intrautérine.
  相似文献   
84.
85.
Background. Little is known about preload-dependent cardiac function after brain death (BD) and subsequent graft preservation.

Methods. A validated model of BD in rabbits was developed and myocardial performance was studied after BD induction and 1 hour of subsequent global hypothermic ischemia using a validated rabbit model and an isolated work-performing heart preparation.

Results. Significant decreases in stroke work, left ventricular contractility, and left ventricular relaxation were observed 2 hours after BD. After global hypothermic ischemia, significant decreases in stroke work, left ventricular contractility, and left ventricular relaxation were observed in the BD group compared with controls. Cardiac output and coronary flow were also significantly decreased in BD hearts compared with controls. Creatine kinase release was increased by 32.5% in BD hearts compared with controls.

Conclusions. In a rabbit model, BD combined with global hypothermic ischemia causes a significant decrease in left ventricular function compared with global hypothermic ischemia. This dysfunction may be attributed to a significant decrease in coronary flows in BD hearts.  相似文献   

86.
Prior to 1975, Stingy Run was a third-order tributary of Kyger Creek, which empties into the Ohio River at Mile 260 (Gallia County, Ohio). Both streams drained strip mine refuse areas and physicochemical measurements indicated acidicmine drainage conditions (e.g., low pH). A depauperate macroinvertebrate community, dominated by a few acid-tolerant taxa, was found in both streams and no fishes were collected. In 1974, Stingy Run was impounded to form a fly ash pond which contains fly ash sluiced from Ohio Power Company's General James M. Gavin coal-fired power plant. Physicochemical and biological sampling during 1975–1986 indicated marked changes in the aquatic ecology of Stingy Run between 1) pre-impoundment and post-impoundment conditions; and 2) effluent pH control treatments after impoundment. Fly ash discharge eliminated acidicmine drainage characteristics in Stingy Run and lower Kyger Creek. After impoundment, net spinning caddisflies and a few dipteran taxa dominated the Stingy Run benthic community, reflecting changes in functional niches likely due to improved habitat and greater food availability. Replacement of acid feed by CO2 injection for effluent pH control and changes in ash pond chemistry occurred concomitant with elimination of a substrate floc; increased species richness and densities of invertebrates were subsequently observed. In Stingy Run, species richness and diversity of fishes increased from 1983 to 1986, reflecting improved water quality and increased benthic production after impoundment. Many of these fishes are opportunistic feeders on drifting insects.  相似文献   
87.
The diameter of the temporal superior and inferior retinal artery and vein were measured at the optic disk border and 2 mm from the disk center in 264 nonselected normal eyes on the basis of photographs, with correction of magnification. Additionally, the individual ocular magnification factor was determined by Littmann's method. The mean caliber of the artery was 0.113 +/- 0.019 mm at the disk border and 0.118 +/- 0.023 2 mm from the disk center. The corresponding values for the vein were 0.149 +/- 0.026 mm and 0.159 +/- 0.026 mm. The correlations between vessel caliber and disk size were not significant, but the relationship between disk size and the quotient of vessel diameter divided by disk size was highly significant (p less than 0.0001). Vessel diameter can therefore be taken as an independent unit for determining optic disk size in relative and approximately also in absolute units. Thus, mean horizontal disk diameter (1.77 +/- 0.33 mm) corresponded to 16.3 +/- 3.5 artery and 12.3 +/- 2.6 vein diameters (measured at the optic disk border). The mean individual ocular magnification factor was 0.302 +/- 0.017, with a Gauss standard distribution. If the optical characteristics of a photographed eye are not known and the ocular magnification factor is assumed to be 0.302, then 68.3% of all eyes will be covered with an inaccuracy of 5.6% and 95.5% of all eyes with an inaccuracy of 11.2%.  相似文献   
88.
Four controlled-release nifedipine products were investigated in two clinical studies. In study 1, 22 healthy male volunteers took part in an open, multiple-dose, randomized, crossover study to determine the relative bioavailablity of two 10 mg controlled-release nifedipine tablet (Adalat® Retard, Bayer), administered 12 hourly, and one 20 mg controlled-release nifedipine tablet (Adalat® Retard, Bayer) administered 12 hourly. In study 2, 24 healthy male volunteers took part in an open, multiple-dose, randomized, three-period, crossover study to determine the relative bioavailability of (i) two 30 mg nifedipine gastro-intestinal therapeutic system (GITS) tablets (Adalat® XL, Bayer) administered once daily; (ii) one 60 mg nifedipine GITS tablet (Adalat® XL, Bayer) administered once daily; and (iii) one 20 mg plus one 10 mg nifedipine controlled-release tablet (Adalat® Retard, Bayer), administered 12 hourly. In both studies detailed pharmacokinetic data, in particular with respect to the controlled-release characteristics of the different formulations, were collected. Results of both studies indicate that all nifedipine products investigated are bioequivalent with respect to the extent of absorption of nifedipine. The nifedipine GITS products (Adalat® XL) have better controlled-release properties than the Adalat® Retard product, and are suitable for once-a-day administration.  相似文献   
89.
The Authors are reviewing their experience of Obstructive Uropathies diagnosed and treated surgically in neonates, the last 8 years in their Institution. 67 cases were reviewed, in which 37 presented with ureteropelvic junction obstruction (UPJ). 13 with posterior urethral valves, 11 with primary megaureter and 6 with ureterocele. Prenatal ultrasonography allowed the diagnosis to be made in two third of the patients. UPJ is the most common obstructive uropathy observed. Posterior urethral valves the most severe because of high pulmonary and renal (dysplasia) complication rate. Surgery, when indicated, has no more complications to be expected than in general population, if oriented prophylactic measures are taken in the early peri- and postoperative period.  相似文献   
90.
Lipodermatosclerosis is a sign of severe chronic venous insufficiency. In this stage of CVI one can find capillary leakage of water and plasmaproteins which results in a higher capillary filtration rate. In skin biopsies the result of this process can be seen as a pericapillary halo. The group of Burnand recently described fibrinogen deposits in this area. We studied the capillaries and their surrounding tissue to determine the thickness of the collagen IV deposits. In severe CVI with lipodermatosclerosis a significant increase of the collagen IV layer was observed. Collagen IV thickness was measured by an index method. The collagen IV thickness for this purpose refers to the capillary diameter. It can be suggested that the increase of the venous pressure in the capillaries leads to leakage of several proteins and namely fibrinogen. As a result of the increase of fibrinogen the collagen IV layer becomes thicker which leads to a decreasing function of the capillaries. In this way an auto-amplification mechanism maintains CVI. An other explanation can be induction of collagen IV due to the high capillary pressure in CVI.  相似文献   
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