全文获取类型
收费全文 | 794篇 |
免费 | 123篇 |
国内免费 | 33篇 |
专业分类
耳鼻咽喉 | 5篇 |
儿科学 | 83篇 |
妇产科学 | 5篇 |
基础医学 | 229篇 |
口腔科学 | 2篇 |
临床医学 | 51篇 |
内科学 | 275篇 |
皮肤病学 | 3篇 |
神经病学 | 24篇 |
特种医学 | 62篇 |
外科学 | 64篇 |
综合类 | 21篇 |
预防医学 | 56篇 |
眼科学 | 3篇 |
药学 | 35篇 |
中国医学 | 1篇 |
肿瘤学 | 31篇 |
出版年
2022年 | 7篇 |
2021年 | 4篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 10篇 |
2017年 | 9篇 |
2016年 | 7篇 |
2015年 | 17篇 |
2014年 | 12篇 |
2013年 | 24篇 |
2012年 | 25篇 |
2011年 | 28篇 |
2010年 | 23篇 |
2009年 | 27篇 |
2008年 | 33篇 |
2007年 | 51篇 |
2006年 | 38篇 |
2005年 | 32篇 |
2004年 | 27篇 |
2003年 | 27篇 |
2002年 | 38篇 |
2001年 | 49篇 |
2000年 | 36篇 |
1999年 | 30篇 |
1998年 | 31篇 |
1997年 | 24篇 |
1996年 | 18篇 |
1995年 | 17篇 |
1994年 | 19篇 |
1993年 | 19篇 |
1992年 | 15篇 |
1991年 | 14篇 |
1990年 | 21篇 |
1989年 | 21篇 |
1988年 | 20篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 13篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 17篇 |
1981年 | 6篇 |
1980年 | 7篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 5篇 |
1976年 | 8篇 |
1975年 | 4篇 |
1973年 | 6篇 |
1972年 | 4篇 |
排序方式: 共有950条查询结果,搜索用时 10 毫秒
1.
Two modified helical basket extractors are described that have increased the success rate of removing ureteral calculi using fluoroscopy from 63% to 92%. Initially a rather stiff and expandable basket with a 20-cm filiform tip is used with coaxial catheters and sheath (stage 1). If this procedure is unsuccessful, a basket with two long cable ends is passed from the nephrostomy out through the urethra (stage 2). When used with coaxial bladder catheters, this technique allows dilatation of the vesicoureteric junction and retrograde catheterization and injection of fluids or gas to dislodge the stone prior to extraction. In a series of 38 patients, stones were removed in all but three (a success rate of 92%). In five cases small stones (less than 5 mm) were not retrieved but subsequent studies were normal. Ureteral stones were found in the abdominal ureter in 28 cases, in the pelvic ureter in seven cases, and in multiple sites in three cases. Stones were larger than 1 cm in 27.7% of cases. Postextraction mucosal edema with reduced ureteral patency was common but usually cleared in 2-3 days. Occasional complications were related to the nephrostomy. 相似文献
2.
3.
Retrorenal colon: implications for percutaneous diskectomy 总被引:1,自引:0,他引:1
It has been recommended that computed tomography (CT) with the patient prone be performed in every patient undergoing percutaneous diskectomy; this would enable detection of a retrorenal location of the colon, which could interfere with the percutaneous procedure. In this evaluation of 346 prone CT studies, only one patient (0.29%) was found to have retrorenal or retropsoas bowel that would have been perforated at diskectomy. Because of this extremely low prevalence, the performance of prone CT in every patient undergoing percutaneous lumbar diskectomy is not believed to be necessary. 相似文献
4.
Measurements of respiratory mechanics are frequently made in ventilated infants and children. Esophageal pressure measurements (Pes using a balloon on a catheter have been used to partition the respiratory mechanics into lung and chest wall components. Appropriate positioning of this balloon is crucial to obtain accurate estimates of pleural pressure. Traditionally, in spontaneously breathing subjects the balloon position is assessed with an occlusion test. In ventilated subjects, it is not always possible to perform an occlusion test prior to paralysis, and even if such a test is performed it may not be relevant under conditions of positive pressure ventilation. We have assessed a positive pressure occlusion test that is suitable for paralyzed subjects. By occluding the airway opening and applying gentle pressure to the abdomen or rib cage, positive swings in pressure can be measured by both Pes and airway opening pressure (Pao). We compared traditional occlusion tests measured in 16 spontaneously breathing puppies to the positive pressure occlusion test performed after paralysis. In 2 pups we were unable to obtain a reasonable traditional occlusion test (>15% difference between Pes and Pao) but we obtained 10 traditional occlusion tests in each of the remaining 14 pups (2.1–14 kg). In 11 of these animals Ape, was within 10% of Pao. This compared well to positive pressure occlusion test using abdominal pressure performed after paralysis, where Apes was within 10% of ΔPao in 10 animals. In 9 of these pups occlusion tests were also performed by applying pressure on the rib cage, where ΔPes was within 10% of ΔPao in 6 animals. These results suggest that it is possible to perform accurate occlusion tests in paralyzed subjects by abdominal or rib cage compression with the airway occluded. Pediatr Pulmonol. 1994; 17:56–62. © 1994 Wiley-Liss, Inc. 相似文献
5.
6.
The lethal effects of lambda infection and lambda induction were studied using conditional lethal mutants of phage lambda in the su- host W3350. Phage with mutations in Q and R, which are blocked after DNA replication, kill promptly and efficiently on induction or infection. Infection with mutants defective in O and P, which do not replicate, kills less efficiently, although these mutants do kill effectively at high multiplicity of infection. Heat induction of lysogens carrying DNA defective mutants O or P promptly arrests host DNA synthesis, but this leads to killing only after a considerable lag. Heating also blocks transfer of an F-gal episome by a lysogen in which a temperature inducible O or P mutant is carried on the episome. These effects of heating are reversed by cooling, which leads to recovery of host DNA synthesis and recovery of the ability to transfer the episome. The effects of heating lysogens for temperature inducible DNA defective phage are interpreted to result from interruption of the Escherichia coli chromosome (or episome), which in itself, is not lethal to the host. Their reversal on cooling is attributed to repair of the break in the chromosome, which permits survival, often associated with curing. Evidence is presented that interruption of the E. coli chromosome can also be produced by infection, but the relationship of this event to loss of viability on infection is still uncertain. N mutants kill even less efficiently than O and P mutants on infection and show killing and DNA arrest on thermal induction only after an initial stimulation of DNA synthesis. They neither cure appreciably, nor resume DNA synthesis on cooling, once DNA synthesis is arrested. Not all the properties of N mutants can presently be explained. 相似文献
7.
Peiwen Pan Mari Leppilampi Silvia Pastorekova Jaromir Pastorek Abdul Waheed William S. Sly Seppo Parkkila 《The Journal of physiology》2006,571(2):319-327
Using real-time PCR and immunohistochemistry, we have examined the expression of carbonic anhydrase isozymes (CA) I, II, III, IV, IX, XII, XIII and XIV in the brain, kidney, stomach and colon of the wild-type, CA II-deficient ( Car2−/− ), and CA IX deficient ( Car9−/− ) mice. The expression of Car4, Car12, Car13 and Car14 mRNAs did not show any significant deviations between the three groups of mice, whereas both groups of CA deficient mice showed decreased expression levels of Car1 in the colon and Car3 in the kidney. The Car2 mRNA level was greatly reduced but not completely abolished in all four tissues from the Car2−/− mice in which no CA II protein was expressed. Sequencing the Car2 cDNA isolated from C57BL6 Car2−/− mice revealed two nucleotide differences from the wild-type C57BL6 mice. One is a silent polymorphism found in Car2 mRNA from wild-type DBA mice, which is the strain that provided the original mutagenized chromosome. The second change is a mutation that causes prematurely terminated translation at codon 155 (Gln155X). Car9 mRNA and CA IX protein expression levels were up-regulated about 2.5- and 3.6-fold, respectively, in the stomach of the Car2−/− mice. These results suggest that the loss of function of cytosolic CA II in the stomach of Car2−/− mice leads to up-regulation of an extracellular CA, namely CA IX, which is expressed on the cell surface of the gastric epithelium. 相似文献
8.
Holt PG Sly PD Martinez FD Weiss ST Björkstén B von Mutius E Wahn U 《Nature immunology》2004,5(7):695-698
The spiraling costs of asthma treatment seem set to continue rising, given the equivocal performance of the latest generation of specific anti-inflammatory drugs in trials in adult asthmatics. We argue that the continuation of this trend is inevitable unless there is a substantial realignment of entrenched drug development policy in the pharmaceutical industry and a parallel shift in licensing policy by regulatory authorities to encourage the development of drugs capable of halting the progression from acute to chronic asthma when the disease first manifests in childhood. The theoretical framework for such an approach, including proof-of-principle data from studies in children with early-stage disease and a range of candidate drugs, already exists. What is needed is informed debate on the risks versus potential benefits of this approach. 相似文献
9.
Glycoproteins present in human follicular fluid that inhibit the zona- binding capacity of spermatozoa 总被引:1,自引:0,他引:1
Previous studies have suggested that human follicular fluid contains
factors that reduce the zona-binding capacity of spermatozoa. The present
study provides further evidence of the existence of such factors. Using the
hemizona binding assay (HZA), we have shown that the inhibitory effect of
human follicular fluid on the zona-binding capacity of spermatozoa is
concentration-dependent, an inhibitory effect being detected when the
concentration of human follicular fluid was > or = 10%. A 1%
concentration of human follicular fluid did not possess this inhibitory
activity. Heating human follicular fluid at 56 degrees C for 30 min did not
affect its inhibitory properties; treatment with proteinase-K abolished
such inhibition. Human follicular fluid was fractionated sequentially by
concanavalin-A affinity chromatography, Mono Q ion-exchange chromatography
and Superose-12 gel filtration. The zona binding inhibitory activity
resided in the fraction which bound to the lectin and Mono Q column and
contained molecules with native molecular weights of 32 and 192 kDa. Sodium
dodecyl sulphate-polyacrylamide gel electrophoresis analysis suggested that
the 192 kDa glycoprotein was a tetramer, while the 32 kDa glycoprotein
remained as a single molecular species under denaturing conditions. We
conclude that two glycoproteins were responsible for the zona binding
inhibitory activity of human follicular fluid. The physiological role of
these factors remains unclear.
相似文献
10.
R. Michael Sly John A. Anderson C. Warren Bierman Paul Chervinsky Frederick C. Cogen James G. Easton Israel Glazer James P. Kemp Allan Knight Richard A. Krumholz Richard A. Nicklas Burton M. Rudolph Diane E. Schuller Allen T. Segal R. Michael Sly Stanley J. Szefler Michael J. Welch Ned J. Whitcomb Minoru Yamate 《The Journal of allergy and clinical immunology》1985,75(4):443-449