全文获取类型
收费全文 | 1568738篇 |
免费 | 146761篇 |
国内免费 | 6226篇 |
专业分类
耳鼻咽喉 | 20175篇 |
儿科学 | 51165篇 |
妇产科学 | 41152篇 |
基础医学 | 232407篇 |
口腔科学 | 45861篇 |
临床医学 | 154177篇 |
内科学 | 313756篇 |
皮肤病学 | 36464篇 |
神经病学 | 135889篇 |
特种医学 | 54102篇 |
外国民族医学 | 375篇 |
外科学 | 215872篇 |
综合类 | 35455篇 |
现状与发展 | 3篇 |
一般理论 | 534篇 |
预防医学 | 135099篇 |
眼科学 | 33884篇 |
药学 | 117807篇 |
59篇 | |
中国医学 | 6838篇 |
肿瘤学 | 90651篇 |
出版年
2021年 | 16646篇 |
2020年 | 14345篇 |
2019年 | 24941篇 |
2018年 | 29538篇 |
2017年 | 25206篇 |
2016年 | 26577篇 |
2015年 | 29731篇 |
2014年 | 36445篇 |
2013年 | 50192篇 |
2012年 | 61363篇 |
2011年 | 64206篇 |
2010年 | 42094篇 |
2009年 | 35468篇 |
2008年 | 55440篇 |
2007年 | 57186篇 |
2006年 | 56760篇 |
2005年 | 54448篇 |
2004年 | 51154篇 |
2003年 | 48379篇 |
2002年 | 46604篇 |
2001年 | 64950篇 |
2000年 | 66777篇 |
1999年 | 55134篇 |
1998年 | 15449篇 |
1997年 | 13907篇 |
1996年 | 13736篇 |
1995年 | 12988篇 |
1994年 | 12065篇 |
1993年 | 11289篇 |
1992年 | 42664篇 |
1991年 | 41743篇 |
1990年 | 40335篇 |
1989年 | 38206篇 |
1988年 | 35325篇 |
1987年 | 34406篇 |
1986年 | 32863篇 |
1985年 | 31316篇 |
1984年 | 23604篇 |
1983年 | 20050篇 |
1982年 | 12064篇 |
1979年 | 21373篇 |
1978年 | 15160篇 |
1977年 | 12362篇 |
1976年 | 12194篇 |
1975年 | 12446篇 |
1974年 | 15277篇 |
1973年 | 14907篇 |
1972年 | 13704篇 |
1971年 | 12742篇 |
1970年 | 11840篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Changing attentional demands in left hemispatial neglect. 总被引:1,自引:0,他引:1
R F Kaplan M Verfaellie M E Meadows L R Caplan M S Pessin L D DeWitt 《Archives of neurology》1991,48(12):1263-1266
Seven variations of a letter cancellation test were used to examine how varying attentional demands affect hemispatial neglect in patients with right hemisphere lesions. While the 14 targets always remained in the same location, the number of distractors (zero, nine, 28, or 82) as well as their complexity (one letter or nine different letters) were varied. The percentage of targets canceled in the left hemispace was linearly related to the number of distractors. There were no differences between the complexity conditions. In a second study, the same 14 targets were presented but the distractors (zero, 14, or 41) were all placed on the right. Increasing the number of distractors on the right increased neglect on both sides of the space. Taken together, these results suggest that, while the limited attentional resources of the left hemisphere are biased toward the right hemispace, the absence of contralateral attentional demands allows these resources to be directed ipsilaterally. 相似文献
993.
S C Chua A W Brown J Kim K L Hennessey R L Leibel J Hirsch 《Brain research. Molecular brain research》1991,11(3-4):291-299
We have used a novel method to identify genes expressed in the hypothalamus which may be potentially involved in controlling food intake and energy metabolism. We assumed that food deprivation, a powerful stimulus of food intake, would stimulate the activity of neural pathways involved in feeding behavior which should be reflected in an increase in the synthesis of any relevant neuropeptide and its messenger RNA. A study of 5 neuropeptides in 5 strains of mice has identified neuropeptide Y (NPY) as a gene whose expression in the hypothalamus is controlled by nutritional status, suggesting that hypothalamic NPY neurons are a link in the neural network regulating feeding behavior and energy metabolism. In addition, we have studied the effect of the diabetes mutation on neuropeptide gene expression during fasting and refeeding. Our findings suggest that abnormal NPY and enkephalin gene expression in the hypothalamus may be two important determinants of the expression of the diabetes mutation. 相似文献
994.
B Djuricic S R Olson H M Assaf T S Whittingham W D Lust L R Drewes 《Journal of cerebral blood flow and metabolism》1991,11(2):308-313
Free choline and ATP contents were measured in Mongolian gerbil hippocampal slices (tissue) and incubation media (media) during exposure to 30 min of aglycemia, high potassium, anoxia, or ischemia. Changes in choline levels reflected the degree of energy reduction, lower ATP levels being associated with high choline (4-fold increase during exposure to high potassium and anoxia, and 11-fold increase during ischemia). Media (extracellular) choline was particularly affected and increased about twofold during relatively mild energy depletion (e.g., aglycemia), but tissue choline content was less sensitive to energy reduction. A plot of choline vs. ATP levels indicated a nonlinear correlation, and the sharp increase in choline occurred when ATP values fell to about 2.5 nmol/mg of protein. Inhibition of acetylcholine sterase by 10 microM physostigmine during ischemia did not prevent an increase in choline contents but rather enhanced them, indicating that acetylcholine hydrolysis was not the source of free choline. Formation of free choline was Ca2+ independent. These findings suggest the involvement of phospholipase D and phosphatidylcholine hydrolysis in free choline formation during energy stress. The extent of choline formation may be an indicator of the degree of membranal damage, which in turn reflects damage to the metabolic machinery of the cell. 相似文献
995.
M. L. Hernández J. J. Fernández-Ruiz R. de Miguel J. A. Ramos 《Journal of neural transmission (Vienna, Austria : 1996)》1991,83(1-2):77-84
Summary In this work, we have studied the time-course of the effects of pharmacological administration of ovarian steroids on tyrosine hydroxylase (TH) activity in the limbic forebrain of ovariectomized rats. Administration of estradiol produced a late decrease in TH activity. This effect was found 24 hours after the last steroid injection, disappearing at 32 hours. It was antagonized by progesterone, since a single injection of this steroid to estradiol-pretreated rats reversed to control values the estradiol-induced decrease. Nevertheless, the administration of progesterone after estradiol treatment caused a short-time decrease in the limbic activity of TH, which was observed 4 hours after the last steroid injection, disappearing subsequently. On the other hand, the administration of progesterone alone produced a biphasic effect, with a reduction at 24 hours, followed by an increase at 32 hours. These effects were only observed in the animals non-treated with estradiol, disappearing with a previous treatment with estrogens. Hence, it can be concluded that both ovarian steroids may affect the limbic TH activity. Thus, estradiol produced a late inhibitory effect on the activity of this enzyme, which was antagonized by progesterone. Administration of the last one to estradiol-treated rats produced a short-time inhibitory effect, whereas its administration to non-treated rats produced a late biphasic effect (inhibition followed by stimulation), which was not observed in estradiol-treated rats. 相似文献
996.
Melatonin, a pineal hormone, released photoperiodically, was administered systemically in rats, previously implanted with semimicroelectrodes into six different brain structures. The multiunit electrical activity of these structures was recorded for 10 min before and 60 min after melatonin administration in unanesthetized, freely moving rats. Different melatonin doses (100, 200, 500, and 1000 micrograms/kg) produced changes in the electrical activity of all tested structures. However, amygdala, rostral hypothalamus and mesencephalic reticular formation showed the most important changes. The main effect induced by melatonin was a dose-related decrease of the spontaneous electrical activity. The significance of these effects is discussed within the context of the behavioral and endocrinological effects of melatonin. 相似文献
997.
Toxic effects of colloids in the intensive care unit. 总被引:4,自引:0,他引:4
Colloid fluid solutions are frequently used as plasma volume expanders in the critically ill. As a group, these nonblood volume replacement solutions have in common a number of potential adverse effects. Intravascular volume overload, dilutional coagulopathy, extravascular extravasation across leaky capillary membranes, and anaphylactoid reactions may all occur with administration of any colloid. In addition, individual agents have unique toxic effects. Renal dysfunction has been associated with dextran 40, myocardial depression with albumin, hypotension with purified plasma protein, and hyperamylasemia with hetastarch. Because no ideal colloidal solution exists, knowledge of type, severity, and clinical significance of adverse effects is important in determining the appropriate plasma volume expander and monitoring its effects. 相似文献
998.
R S Desowitz K K Shida L Pang G Buchbinder 《The American journal of tropical medicine and hygiene》1989,41(6):630-634
This study characterizes a Plasmodium berghei white rat model of P. falciparum malaria in the pregnant human. Seventy-day-old and 114-day-old female rats, given an infecting inoculum at time of mating, had higher parasitemias and a more severe anemia than age- and sex-matched controls. Under these experimental conditions, the parasitemia went to crisis in all animals and there were no fatal infections. In contrast, all animals died when the infection was initiated 7 days after conception, a timing that brought a coincidence of peak parasitemia and term. Pregnancy during the post-crisis subpatent period did not cause recrudescence. At the time of delivery, the parasitemia was consistently higher in the placental (crush smear) blood than in the peripheral (tail) blood. This difference was greatest in animals giving birth shortly before or 1-2 days after the parasitemic crisis. Very young, compact parasite forms predominated in the placental blood, whereas trophozoites predominated in the peripheral blood. 相似文献
999.
Methodological Issues Associated with an Audit of Stillbirth in a Family Medicine Practice in Israel
An audit of deficient outcome involves the step-by-stepanalysis of every event preceding the occurrence of a preventablemedical outcome in order to determine exactly what went wrong.This paper describes methodological problems and related issuesassociated with a deficient outcome audit undertaken on fivestillbirths which occurred in a rural family medical practiceIsrael between 1985 and 1987. Problems included initial officialdisinterest towards the audit, and the high levels of suspicionand antagonism which it aroused in hospital staff approachedfor information. The problematic aspect of such audits needsmore attention. The importance of this type of audit for establishing the precisereasons for perinatal deaths, and thus for maintaining antenatalcare standards is discussed. In view of the small numbers ofsuch events likely to occur within any one family practice itis not only feasible but also desirable for more family doctorsto carry out such audits routinely, despite the difficultieswhich are involved. 相似文献
1000.