全文获取类型
收费全文 | 26586篇 |
免费 | 2194篇 |
国内免费 | 53篇 |
专业分类
耳鼻咽喉 | 218篇 |
儿科学 | 867篇 |
妇产科学 | 679篇 |
基础医学 | 3577篇 |
口腔科学 | 445篇 |
临床医学 | 3631篇 |
内科学 | 4556篇 |
皮肤病学 | 371篇 |
神经病学 | 2986篇 |
特种医学 | 747篇 |
外科学 | 2708篇 |
综合类 | 480篇 |
一般理论 | 43篇 |
预防医学 | 3560篇 |
眼科学 | 581篇 |
药学 | 1694篇 |
中国医学 | 20篇 |
肿瘤学 | 1670篇 |
出版年
2023年 | 179篇 |
2022年 | 260篇 |
2021年 | 524篇 |
2020年 | 324篇 |
2019年 | 522篇 |
2018年 | 604篇 |
2017年 | 464篇 |
2016年 | 462篇 |
2015年 | 578篇 |
2014年 | 765篇 |
2013年 | 1187篇 |
2012年 | 1720篇 |
2011年 | 1794篇 |
2010年 | 935篇 |
2009年 | 831篇 |
2008年 | 1585篇 |
2007年 | 1661篇 |
2006年 | 1756篇 |
2005年 | 1630篇 |
2004年 | 1477篇 |
2003年 | 1377篇 |
2002年 | 1375篇 |
2001年 | 389篇 |
2000年 | 333篇 |
1999年 | 365篇 |
1998年 | 324篇 |
1997年 | 261篇 |
1996年 | 222篇 |
1995年 | 185篇 |
1994年 | 204篇 |
1993年 | 204篇 |
1992年 | 255篇 |
1991年 | 232篇 |
1990年 | 205篇 |
1989年 | 216篇 |
1988年 | 195篇 |
1987年 | 202篇 |
1986年 | 203篇 |
1985年 | 211篇 |
1984年 | 181篇 |
1983年 | 171篇 |
1982年 | 156篇 |
1981年 | 122篇 |
1980年 | 151篇 |
1979年 | 133篇 |
1978年 | 130篇 |
1977年 | 123篇 |
1975年 | 108篇 |
1974年 | 116篇 |
1973年 | 103篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
V V Joshi A B Cantor G Altshuler E W Larkin J S Neill J J Shuster C T Holbrook F A Hayes R Nitschke M H Duncan 《Cancer》1992,69(8):2197-2211
Histologic sections (minimum of four sections per patient) from 211 patients with neuroblastoma were reviewed. The tumors were resected before therapy, which was standardized according to age and stage. Low mitotic rate (MR) (less than or equal to ten per ten high-power fields) and calcification emerged as the most significant prognostic features after statistical analysis by stepwise log-rank tests (P less than 0.0001 and P = 0.0065, respectively). Histologic Grades 1, 2, and 3 were defined on the basis of the presence of both, any one, or none of these two prognostic features, respectively (Grade 3 had absence of low MR, i.e., these tumors had high MR [greater than ten per ten high-power fields]). Statistically significant differences in survival were observed in the grades after adjusting for age and stage (P less than 0.001). The degree of differentiation, although significant by itself, was no longer significant after adjusting for the grades. Age groups (less than or equal to 1 versus greater than 1 year of age), which also emerged as an independent prognostic feature (P less than 0.001), were linked with the grades to define two risk groups as follows: (1) a low-risk (LR) group consisting of patients in both age groups with Grade 1 tumors and patients 1 year of age or younger with Grade 2 tumors and (2) a high-risk (HR) group consisting of patients older than 1 year of age with Grade 2 tumors and patients in both age groups with Grade 3 tumors. The difference in survival between LR (160 cases) and HR groups (51 cases) was statistically significant (P less than 0.001). Concordance between these LR and HR groups and the Shimada classification was observed in 84% of cases. The new histologic grading system has the following advantages: (1) use of familiar terminology and histologic features in the grading system and (2) relative ease of assessment because the degree of differentiation does not need to be determined. The grading system should be tested on a new data set with an appropriate histologic sample of similar size to confirm these results. 相似文献
52.
A retrospective review of 23 patients with osteoblastoma was undertaken in an attempt to answer questions concerning the aggressiveness and potential malignancy of this tumour. Demographic information confirmed that recorded in the literature. There was no suggestion of malignant potential, but, significantly, one tumour persisted, with local recurrence after 11 operations over a period of 27 years. A second tumour, a spinal lesion, occurred (still in a benign form) after a symptom-free period of 17 years. Recognition of aggressive features clinically, radiologically and histologically suggests the need for more aggressive surgical treatment, and late recurrence indicates the need for a more guarded prognosis and longer follow-up. 相似文献
53.
Iliac-vessel injury from total hip arthroplasty is associated with hemorrhagic complications and an increased death rate. The authors identified seven patients who had severe medial displacement of the acetabular prosthesis and associated vascular injury to the iliac vessels after total hip replacement. One patient had two hip replacements. Preoperative findings included a pelvic mass (three hips), pelvic pain (eight), radiologic evidence of cement in the pelvis (three) and the acetabular prosthesis in the pelvis (eight), computed tomographic evidence of cement in the pelvis and proximity of the prosthesis to the iliac vessels (four), and arteriography showing displacement or compression of the iliac vessels (seven). Operative management in all cases involved medial exposure, mobilization and repair of the iliac vessels before revision of the hip prosthesis. Postoperative complications were deep vein thrombosis (three), in spite of prophylaxis, and occlusion of a vein interposition graft (one) requiring placement of a femoral crossover graft. There were no deaths, amputations or hemorrhagic complications. The authors advocate preoperative identification of patients who have iliac-vessel involvement by their total hip prosthesis and initial medial extraperitoneal exposure and repair of these vessels before removal of the displaced acetabular prosthesis. 相似文献
54.
Ruth Ladurner Gerald Brandacher Wolfgang Steurer Stefan Schneeberger Claudia Bösmüller Martin Clemens Freund Alfons Kreczy Alfred Königsrainer Raimund Margreiter 《Transplant international》2003,16(12):885-889
Fungal infections still represent a serious complication after organ transplantation. Early diagnosis and aggressive treatment are crucial. Because of the many diagnostic problems involved, we present a case of mucormycosis--primarily affecting the paranasal sinuses with later intracranial extension--in a highly immunized recipient of a third renal transplant. Although fungal infection was suspected from various imaging techniques, only the detection of typical fungal hyphae in the infected tissue was diagnostic. Neither the blood tests and cerebrospinal fluid examinations performed nor cultures from maxillary sinus fluid were of any diagnostic help. Surgical debridement from a transnasal as well as an intracranial approach and systemic amphotericin B together with the discontinuation of immunosuppression after removal of the rejected graft were able to save the patient. This case stresses the importance of early diagnosis that can only be made from tissue biopsies and allows appropriate timely treatment. 相似文献
55.
56.
R W Lambert J A Martin G J Thomas I B Duncan M J Hall E P Heimer 《Journal of medicinal chemistry》1989,32(2):367-374
Phosphonoacetic acid (PAA, 1) was coupled with various acyclonucleosides, 2'-deoxyuridines, cytidines, and arabinosyluracils, with 2,4,6-triisopropylbenzenesulfonyl chloride (TPS) or dicyclohexylcarbodiimide (DCCI) as condensing agents, to give a range of phosphonate esters. The carboxylic ester linkage of PAA to the 5'-position of 5-bromo-2'-deoxyuridine (BUdR, 3) was achieved via the mixed anhydride formed from (diethylphosphono)acetic acid and trifluoroacetic anhydride. Phosphonoformic acid (PFA, 2) was coupled with BUdR by using the DCCI method to give the phosphonate ester. Of these compounds only phosphonate esters in the 2'-deoxyuridine series showed significant activity against herpes simplex virus types 1 and 2. The BUdR-PAA derivative and the BUdR-PFA derivative were highly active, especially the latter, which was more active than the parent nucleoside BUdR against the type 2 virus. The active compounds may exert their effects by extracellular or intracellular hydrolysis to the corresponding antiviral agents, but an intrinsic component of antiviral activity may also be involved. 相似文献
57.
A review of strategies for enhancing the completeness of notifiable disease reporting. 总被引:1,自引:0,他引:1
Notifiable disease surveillance systems provide essential data for infectious disease prevention and control programs at the local, state, and national levels. Given that reporting completeness is known to vary considerably, this review identifies methods that can reliably enhance completeness of reporting. These surveillance-related activities include initiating active surveillance when appropriate; implementing automated, electronic laboratory-based reporting; strengthening ties with clinicians and other key partners in notifiable disease reporting; and increasing the use of laboratory diagnostic tests in identifying new cases. Despite ample data in support of these strategies, notifiable disease surveillance continues to receive insufficient attention and resources. Recent attention to public health preparedness provides an opportunity to strengthen notifiable disease surveillance and enhance completeness of reporting. 相似文献
58.
Serum concentrations of alkaline phosphatase isoenzymes and osteocalcin in normal pregnancy 总被引:4,自引:0,他引:4
A Rodin A Duncan H W Quartero G Pistofidis G Mashiter K Whitaker D Crook J C Stevenson M G Chapman I Fogelman 《The Journal of clinical endocrinology and metabolism》1989,68(6):1123-1127
We measured serum alkaline phosphatase isoenzymes and osteocalcin levels in 40 healthy women at 4-week intervals throughout uncomplicated pregnancies and 6 weeks after delivery in 17 women. Serum bone alkaline phosphatase was significantly higher in the third trimester than in early pregnancy (P less than 0.001), and this elevation was still apparent at the end of the puerperium, suggesting increased bone turnover. Serum osteocalcin was not detected (less than 0.2 micrograms/L) after the first trimester in the majority of women, and it reappeared within 48 h after delivery. The disappearance of osteocalcin after the first trimester and its rapid reappearance after delivery suggest placental clearance of this peptide. We conclude that serum osteocalcin measurements cannot be used as a marker of bone metabolism during pregnancy. 相似文献
59.
Deep brain stimulation for pain control in humans was first used almost 30 years ago and has continued to receive considerable attention. Despite the large number of clinical reports describing pain relief, numerous studies have indicated that the results of these procedures vary considerably. In addition, many neurosurgeons find the procedures unpredictable, and considerable disagreement still exists regarding important issues related to the technique itself. This review gives an historical overview of the relevant basic and clinical literature and provides a critical examination of the clinical efficacy, choice of stimulation sites, parameters of stimulation, and effects on experimental pain. Finally, we give suggestions for future research that could more definitively determine the usefulness of deep brain stimulation for pain control. 相似文献
60.
Regional extraction of circulating norepinephrine, DOPA, and dihydroxyphenylglycol in humans 总被引:1,自引:0,他引:1
D S Goldstein R O Cannon A Quyyumi P Chang M Duncan J E Brush G Eisenhofer 《Journal of the autonomic nervous system》1991,34(1):17-35
Dihydroxyphenylglycol (DHPG) is the main intraneuronal metabolite of the sympathetic neurotransmitter, norepinephrine (NE), and dihydroxyphenylalanine (DOPA) the immediate product of the rate-limiting step in catecholamine biosynthesis. Simultaneous measurements of regional rates of appearance (spillovers) of NE, DOPA, and DHPG in plasma have the potential to provide unique information about aspects of sympathoneural function but have not actually been measured in humans. In the present study, spillovers of DHPG, DOPA, and NE in the heart, head, leg, and lungs, were estimated from regional extraction fractions of infused [3H]-1-NE, DHPG, and [13C6]DOPA or unlabelled DOPA in humans during cardiac catheterization. There was little cardiac extraction of DHPG (7 +/- SEM 2%) or DOPA (8 +/- 4%) but substantial extraction of NE (69 +/- 4%). Values for cardiac spillover of DHPG and DOPA therefore were similar to values for the arteriovenous increment times plasma flow (arteriovenous production rate), whereas the cardiac spillover of NE averaged about 7-times the NE arteriovenous production rate. Cardiac DHPG spillover (28 +/- 3 ng/min) exceeded the spillovers of NE (9 +/- 2 ng/min) and DOPA (15 +/- 4 ng/min). In contrast, cranial DOPA spillover (159 ng/min) exceeded those of NE and DHPG by 8- and 2-fold and accounted for about 1/10 of the total spillover of DOPA into arterial plasma. In the femoral vascular bed, arteriovenous production rates of NE and DHPG were unrelated to femoral spillovers of NE and DHPG. Arterial and regional clearances of [13C6]DOPA were similar to those of unlabelled DOPA. The results suggest that (1) endogenous NE, DOPA, and DHPG all are released into the bloodstream by the heart, head, and limbs of humans; (2) DHPG and DOPA are not co-released with NE; (3) cardiac arteriovenous production rates of DOPA and DHPG can be used to indicate cardiac spillover of these catechols, whereas the cardiac NE arteriovenous production rate substantially underestimates cardiac NE spillover; and (4) estimates of limb spillover of NE and DHPG require concurrent measurements of the corresponding regional clearances. 相似文献