全文获取类型
收费全文 | 13009篇 |
免费 | 599篇 |
国内免费 | 88篇 |
专业分类
耳鼻咽喉 | 128篇 |
儿科学 | 283篇 |
妇产科学 | 166篇 |
基础医学 | 1559篇 |
口腔科学 | 164篇 |
临床医学 | 906篇 |
内科学 | 3344篇 |
皮肤病学 | 167篇 |
神经病学 | 1121篇 |
特种医学 | 543篇 |
外科学 | 2575篇 |
综合类 | 54篇 |
现状与发展 | 1篇 |
一般理论 | 1篇 |
预防医学 | 255篇 |
眼科学 | 145篇 |
药学 | 837篇 |
中国医学 | 11篇 |
肿瘤学 | 1436篇 |
出版年
2023年 | 95篇 |
2022年 | 168篇 |
2021年 | 260篇 |
2020年 | 166篇 |
2019年 | 211篇 |
2018年 | 260篇 |
2017年 | 206篇 |
2016年 | 279篇 |
2015年 | 291篇 |
2014年 | 367篇 |
2013年 | 430篇 |
2012年 | 693篇 |
2011年 | 763篇 |
2010年 | 476篇 |
2009年 | 437篇 |
2008年 | 742篇 |
2007年 | 817篇 |
2006年 | 770篇 |
2005年 | 783篇 |
2004年 | 783篇 |
2003年 | 698篇 |
2002年 | 690篇 |
2001年 | 262篇 |
2000年 | 246篇 |
1999年 | 249篇 |
1998年 | 161篇 |
1997年 | 124篇 |
1996年 | 131篇 |
1995年 | 96篇 |
1994年 | 105篇 |
1993年 | 85篇 |
1992年 | 191篇 |
1991年 | 152篇 |
1990年 | 170篇 |
1989年 | 152篇 |
1988年 | 156篇 |
1987年 | 137篇 |
1986年 | 125篇 |
1985年 | 110篇 |
1984年 | 72篇 |
1983年 | 70篇 |
1982年 | 33篇 |
1981年 | 40篇 |
1979年 | 45篇 |
1978年 | 37篇 |
1970年 | 32篇 |
1969年 | 36篇 |
1968年 | 26篇 |
1967年 | 29篇 |
1966年 | 28篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Changes in cardiac myosin heavy chain (MHC) gene expression and isozyme transitions have been shown to be caused by developmental changes, hemodynamic overload, or the activity of various hormones. In this study, to examine whether caffeine, which has teratogenic effects on the fetal cardiovascular system, causes the distribution of cardiac MHC phenotype and, if so, to evaluate the mechanisms of the distribution of cardiac MHC phenotype by caffeine, we examined the effects of caffeine, theophylline, and cAMP on the cardiac MHC isoform transitions at the gene and protein levels using hypothyroid adult rats. Furthermore, we examined the expression of alpha- and beta-MHC gene in cardiac muscles of fetuses whose dams had received caffeine. The results showed that caffeine, theophylline, and cAMP caused accumulations of alpha-MHC mRNA and MHC isozyme V1. Furthermore, in the fetal hearts, it was recognized that caffeine induced an accumulation of alpha-MHC gene expression, as was also seen in the dams. However, this effect of caffeine on the heart was stronger in the fetus than in the dam. Intracellular cAMP concentration was increased by the administration of caffeine, theophylline, or cAMP, and the levels showed a positive correlation with those of alpha-MHC mRNA. These results suggest that the induction of alpha-MHC mRNA expression by the administration of caffeine may be induced by an increase in intracellular cAMP concentration. 相似文献
22.
J Hasegawa R Matsuoka K Ichizuka A Sekizawa A Farina T Okai 《Ultrasound in obstetrics & gynecology》2006,27(4):425-429
OBJECTIVES: To evaluate the accuracy of sonographic identification of the site of umbilical cord insertion (CI) at 18-20 weeks of gestation, to compare the sensitivities for detection of a velamentous cord insertion (VCI) secondary to a CI into the anterior, posterior or fundal wall, and to compare the intrapartum complications secondary to VCI into the upper, middle or lower third of the uterus. METHODS: As part of the routine ultrasound scan at 18-20 weeks' gestation we evaluated abnormal CI (VCI and marginal CI) and the location of the CI in the uterus in 3446 pregnancies. In cases of abnormal CI, the location of the CI was further classified as being in the upper, middle or lower third of the uterus. After delivery, the placenta and the umbilical cord were examined and intrapartum complications were compared with the location of the CI. RESULTS: The values for antenatal detection of VCI were: sensitivity, 25 of 40 (62.5%); positive predictive value, 25 of 25 (100%); and negative predictive value, 3406 of 3421 (99.6%). The sensitivity for cases in which the CI was located on the anterior wall was 12 of 13 (92.3%); when it was located on the posterior wall, the sensitivity was 11 of 22 (50.0%); and when it was fundal the sensitivity was 2 of 5 (40.0%). Variable decelerations were frequently observed with a VCI. In lower VCI cases, non-reassuring fetal heart rate patterns and emergency Cesarean sections occurred with a higher frequency than in cases with upper or middle VCI (P < 0.01). After delivery, the length of the aberrant vessels in cases of VCI by pathologic examination was 3.9 +/- 3.3 cm in the upper third, 4.7 +/- 4.6 cm in the middle third, and 10.6 +/- 6.8 cm in the lower third; thus, the aberrant vessel length was significantly greater when the CI was in the lower third of the uterus (P = 0.024). CONCLUSION: We have demonstrated that VCI with a lower CI site and with longer aberrant vessels is associated with various intrapartum complications. This finding has the potential for improving perinatal outcome. 相似文献
23.
Takashi Ito Ryuji Sakakibara MD Tatsuya Yamamoto Tomoyuki Uchiyama Zhi Liu Masato Asahina Morihiro Higashi Kimihito Arai Shoichi Ito Yusuke Awa Kaori Yamamoto Mika Kinou Tomonori Yamanishi Takamichi Hattori 《Clinical autonomic research》2006,16(1):66-71
Abstract Uro-neurological assessment was performed in four patients with small-fiber neuropathy due to amyloidosis (2 transthyretin-type/2
immunoglobulin light-chain-type). Voiding difficulties were due to detrusor weakness and impaired bladder sensation. In two
patients cholinesterase inhibition treatment caused urge incontinence, indicating detrusor denervation supersensitivity. The
underlying mechanisms of urinary dysfunction seem to involve postganglionic cholinergic and afferent somatic nerves. 相似文献
24.
W C Levy A F Jacobson M D Cerqueira D T Matsuoka F H Sheehan J R Stratton 《Journal of nuclear medicine》1992,33(9):1642-1647
The effects of region of interest (ROI) selection and correction for Compton-scattered photons using a buildup factor on radionuclide left ventricular volumes calculated by the Links method were compared in 19 humans with contrast ventriculography and in phantoms. Three different methods of ROI selection were compared: a manual ROI, a second derivative ROI and a 50% count-threshold ROI. In phantoms without Compton scatter correction, volumes were overestimated by 30% (manual ROI), 20% (derivative ROI) and 1% (count threshold ROI). In subjects, results without Compton scatter correction were similar with overestimates of 50% (manual ROI) and 20% (derivative ROI) and an underestimate by 3% (count threshold method). Correction for Compton-scattered photons with the use of a phantom-derived buildup factor resulted in improved accuracy for the manual ROI (+15%) and the derivative ROI (0%). A 50% count threshold ROI following interpolative background subtraction allows the accurate calculation of cardiac volumes without the need for scatter correction, while a second derivative ROI method requires a correction for Compton scatter with the use of a buildup factor. 相似文献
25.
S Matsuoka M Ito T Shinonome M Yoshitoshi A Tanimura 《No shinkei geka. Neurological surgery》1992,20(3):255-259
We reported an autopsy case of a 14-year-old girl with cardiac myxoma, presenting sudden onset of consciousness disturbance and right hemiplegia while running in an 800 meter race. Though CT scan showed no abnormal findings, cerebral angiogram revealed an embolic stenosis of the left middle cerebral artery, and abdominal aortogram showed complete obstruction of the bilateral common iliac artery. Histological study of emboli taken from obstructed femoral arteries showed systemic embolization of the cardiac myxoma. She died three days after admission. Autopsy was performed. Myxoma tissue was not found, but its stalk was left in the left atrial septum. The brain was very edematous, and a myxoma emboli was found in the left middle cerebral artery. Systemic embolization of myxoma to spleen, kidneys, liver, pancreas, etc. was found histologically. Left atrial myxoma is a rare but potentially treatable cause of stroke, and should be included in the differential diagnosis of cerebral vascular disease, especially in young patients. 相似文献
26.
Yoshihide Nagasako Meang Bong Jin Hiroshi Miyazaki Masato Nakayama Tsuyoshi Shimamura Hiroyuki Furukawa Michiaki Matushita Satoru Todo 《Liver transplantation》2006,12(3):435-439
Thrombocytopenia is a frequent finding following living donor hepatectomy. It appears more pronounced in right graft donors than in left graft donors. This study analyzed postoperative thrombocytopenia in 20 living liver donors and examined the change of endogenous thrombopoietin (TPO) in its recovery. Platelet count, TPO level, fibrinogen degradation product (FDP), and D-Dimer were measured before surgery and on postoperative days (PODs) 1, 2, 3, 5, 7, and 14. Concurrently, liver and spleen volumes were calculated by computed tomography. Platelet count on POD 3 was significantly lower in right graft donors than in left graft donors (13.0 +/- 3.7 x 10(4)/microL vs. 16.8 +/- 4.0 x 10(4)/microL, P = 0.039) but recovered by POD 7 in all donors. Postoperative elevations of FDP and D-Dimer were significantly higher in right graft donors than in left graft donors. TPO level rose immediately after surgery, peaked on POD 5 in left graft donors and on POD 7 in right graft donors, and fell nearly to preoperative levels by POD 14. Postoperative TPO level per liver volume was significantly higher in right graft donors than in left graft donors. In conclusion, thrombocytopenia following living donor hepatectomy resolved within the first week regardless of graft type and was mainly associated with increasing consumption of circulating platelets, possibly due to intrahepatic and splenic congestion. With a reduced number of circulating platelets, TPO level rapidly increases. Also, with reduced consumption of platelets related to recovery from surgery, thrombocytopenia should resolve. As a consequence, TPO level would be expected to fall. 相似文献
27.
Kagayaki Kuroda Daisuke Kokuryo Etsuko Kumamoto Kyohei Suzuki Yuichiro Matsuoka Bilgin Keserci 《Magnetic resonance in medicine》2006,56(4):835-843
Referenceless, or self-reference, thermometry is a technique for mapping temperature differences in the region of interest (ROI) using the baseline phase estimated by extrapolating the field in the surrounding region for estimation (RFE) and subtracting the estimated baseline from the measured field. In the present work a self-reference technique based on complex field estimation using 2D polynomials comprising complex-valued coefficients was proposed and optimized. Numerical simulations with a Gaussian-profiled phase distribution demonstrated that the ROI radius had to be 2.3-2.5 times the standard deviation (SD) of the Gaussian function in order to keep the error below 8% of the peak phase change. The area ratio between the ROI and the RFE had to be larger than 2.0 to maintain the error level. Based on the simulations, and phantom and volunteer experiments, the complex-based method with independently optimized polynomial orders for the two spatial dimensions was compared with the phase-based method using the similar-order optimization strategy. The complex-based method appeared to be useful when phase unwrapping was not removed. Otherwise, the phase-based method yielded equivalent results with less polynomial orders. 相似文献
28.
The authors report on 48 patients with calculous pyelonephritis. Urinary obstruction was caused by renal calculi in 21 patients
and ureteral calculi in 27. Urine cultures were positive in 87.5% and bacteremia was seen in 70%. The common organisms in
urine and blood culture wereE. coli, Proteus and Klebsiella. Septic shock occurred in 10 (20.8%) out of 48 patients. Calculous pyelonephritis with urinary obstruction
is a very serious condition. 相似文献
29.
ABSTRACT Embryotoxicity and teratogenicity of cadmium (Cd) and modulation of its effects by N-acetyl-L-cysteine (NAC) were evaluated in mice. Pregnant ICR mice were intraperitoneally injected with 3.5 mg/kg of CdCl2 on day 10 or 11 of gestation (vaginal plug = day 0). Pregnant mice were pretreated with 160 mg/kg of NAC intravenously 2 hours before dosing with CdCl2 . Pregnant mice were killed on day 17 of gestation. Fetuses were examined for external malformations, especially limb malformations, cleft palate and abnormal palatal rugae. There was little difference in body weight gain of dams during the gestation period in the groups treated with NAC plus Cd as compared with the groups treated with Cd alone. Pretreatment with 160 mg/kg of NAC decreased the fetal mortality, incidence of cleft palate and abnormal palatal rugae induced by Cd on day 11. On day 10, pretreatment with NAC decreased the incidence of Cd induced abnormal palatal rugae. These results clearly indicate that NAC exerts protective effects against embryotoxicity and teratogenicity of Cd. 相似文献
30.
Kazuhiko Sonoyama Haruaki Ninomiya Osamu Igawa Yasuhiro Kaetsu Yoshiyuki Furuse Toshihiro Hamada Junichiro Miake Peili Li Yasutaka Yamamoto Kazuhide Ogino Akio Yoshida Shin-ichi Taniguchi Yasutaka Kurata Satoshi Matsuoka Toshio Narahashi Goshi Shiota Yoshihisa Nozawa Hiroaki Matsubara Masatsugu Horiuchi Yasuaki Shirayoshi Ichiro Hisatome 《Hypertension research》2006,29(11):923-934
We examined the effects of angiotensin II (Ang II) on inward rectifier K+ currents (IK1) in rat atrial myocytes. [125I]Ang II-binding assays revealed the presence of both Ang II type 1 (AT1) and type 2 (AT2) receptors in atrial membrane preparations. Ang II inhibited IK1 in isolated atrial myocytes with an IC50 of 46 nmol/l. This inhibition was abolished by the AT, antagonist RNH6270 but not at all by the AT2 antagonist PD123319. Treatment of cells with pertussis toxin or a synthetic decapeptide corresponding to the carboxyl-terminus of Gialpha-3 abolished the inhibition by Ang II, indicating the role of a Gi-dependent signaling pathway. Accordingly, Ang II failed to inhibit IK1 in the presence of forskolin, dibutyryl-cAMP or protein kinase A catalytic subunits. In spite of the increased binding capacities for [125I]Ang II, Ang II failed to affect IKI in cells from spontaneously hypertensive rats (SHR). AT, immunoprecipitation from atrial extracts revealed decreased amounts of Gialpha-2 and Gialpha-3 proteins associated with this receptor in SHR as compared with controls. The reduced coupling of AT, with Gialpha. proteins may underlie the unresponsiveness of atrial IK1 to Ang II in SHR cells. 相似文献