全文获取类型
收费全文 | 265178篇 |
免费 | 21331篇 |
国内免费 | 4644篇 |
专业分类
耳鼻咽喉 | 1646篇 |
儿科学 | 5429篇 |
妇产科学 | 5135篇 |
基础医学 | 27372篇 |
口腔科学 | 5236篇 |
临床医学 | 40952篇 |
内科学 | 32663篇 |
皮肤病学 | 2949篇 |
神经病学 | 16130篇 |
特种医学 | 7318篇 |
外国民族医学 | 2篇 |
外科学 | 20788篇 |
综合类 | 30293篇 |
现状与发展 | 21篇 |
一般理论 | 74篇 |
预防医学 | 32223篇 |
眼科学 | 2600篇 |
药学 | 30986篇 |
222篇 | |
中国医学 | 13546篇 |
肿瘤学 | 15568篇 |
出版年
2024年 | 441篇 |
2023年 | 5064篇 |
2022年 | 6656篇 |
2021年 | 12283篇 |
2020年 | 11217篇 |
2019年 | 11060篇 |
2018年 | 10694篇 |
2017年 | 10876篇 |
2016年 | 10568篇 |
2015年 | 9892篇 |
2014年 | 13572篇 |
2013年 | 18539篇 |
2012年 | 13818篇 |
2011年 | 15766篇 |
2010年 | 10503篇 |
2009年 | 10732篇 |
2008年 | 11881篇 |
2007年 | 12971篇 |
2006年 | 11989篇 |
2005年 | 10795篇 |
2004年 | 9235篇 |
2003年 | 8040篇 |
2002年 | 6269篇 |
2001年 | 5644篇 |
2000年 | 4829篇 |
1999年 | 4124篇 |
1998年 | 3279篇 |
1997年 | 3237篇 |
1996年 | 2956篇 |
1995年 | 2543篇 |
1994年 | 2423篇 |
1993年 | 2005篇 |
1992年 | 1787篇 |
1991年 | 1694篇 |
1990年 | 1464篇 |
1989年 | 1191篇 |
1988年 | 1108篇 |
1987年 | 1017篇 |
1986年 | 937篇 |
1985年 | 1395篇 |
1984年 | 1121篇 |
1983年 | 870篇 |
1982年 | 881篇 |
1981年 | 707篇 |
1980年 | 704篇 |
1979年 | 527篇 |
1978年 | 323篇 |
1977年 | 288篇 |
1976年 | 275篇 |
1975年 | 197篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
941.
S E Irwin G Y Kwei G R Blackburn R Thurman F C Kauffman 《Environmental and molecular mutagenesis》1992,19(3):253-258
Comparison of the mutagenicity of nine isomeric benzo(a)pyrenyl [B(a)P] phenols conjugated with either sulfate or glucuronide was carried out using strain Salmonella typhimurium TA98. Of the nine conjugates tested, only B(a)P-1-sulfate was mutagenic. Accordingly, the mutagenicity of B(a)P-1-sulfate was compared with that of B(a)P and 1-hydroxybenzo(a)pyrene [B(a)P-1-OH] in the presence and absence of rat lung S9 and Aroclor-induced liver S9 with and without an NADPH-generating system. B(a)P-1-sulfate was slightly mutagenic, whereas B(a)P and the 1-hydroxy derivative were nonmutagenic when S9 fractions and NADPH were omitted. Addition of induced liver S9 with NADPH caused mutagenicity with B(a) -1-OH greater than B(a)P greater than B(a)P-1-sulfate. B(a)P-1-sulfate was the only mutagenic species when lung S9 was added. This mutagenicity did not require NADPH. Sodium sulfite, an inhibitor of arylsulfatase, decreased the mutagenicity of B(a)P-1-sulfate. These data suggest that a unique mutagenic species is generated from B(a)P-1-sulfate via arylsulfatase in rat lung. 相似文献
942.
C.C.-W. YU P.A. HALL C.D.M. FLETCHER R.S. CAMPLEJOHN N.H. WASEEM D.P. LANE D.A. LEVISON 《Histopathology》1991,19(1):29-34
Forty-two cases of haemangiopericytoma were studied retrospectively using immunohistochemical staining with PC10, a monoclonal antibody to PCNA. The percentage of tumour cells with positive staining for PCNA was found to correlate well with histological grading. Clinical follow-up data were available in 25 adults and showed no known deaths in 11 cases with a low proportion (less than 14%) of positive cells. Out of 14 cases with a high number (greater than or equal to 14%) of positive cells, seven patients are known to have died, two had metastases, and in a further two there have been multiple recurrences of tumour. DNA flow cytometry was performed on 26 cases but this showed no correlation with PC10 staining or clinical outcome. Staining with PC10 may be of particular value in the identification of patients at greatest risk of rapid tumour metastasis and early death. 相似文献
943.
V. K. Bozhenko E. V. Khmelevskii A. M. Shishkin V. N. Vasil'ev A. G. Zakharov V. I. Kiselev 《Bulletin of experimental biology and medicine》1994,117(3):297-299
The dynamics of125I distribution is studied in rats with induced tumors of the prostate and mammary gland for intravenous administration of125I-3D-G. It is found that 80% of the activity is eliminated in the first 24 hours. A relatively high level of125I accumulation is found in necrotically altered regions of the tumor.
Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 117, № 3, pp. 294–295, March, 1994. 相似文献
944.
Summary
The introduction of fast gradient systems allows a reliable visualization of the extracranial carotid vessels by the magnetic
resonance angiography (MRA) which meanwhile is implemented into clinical routine. By the mainly applied time-of-flight (TOF)
technique, vessels can be imaged without contrast agent (CA). Due to the application of ultra-fast gradient-echo-sequences,
the first-pass evaluation of an intravenous bolus-injection of Gadolinium in the carotids from the aortic arch up to the skull
base can be performed in less than 30 s. In this study, advantages and disadvantages of both techniques are discussed. For
a qualitatively optimal contrast enhanced MRA (CE-MRA) timing parameters like injection delay, flow rate and the adjustment
of sequence parameters have to be considered in relation to the fast venous return from the sinus to the jugular veins. First,
the optimal time point of the data acquisition have been determined at a model and with a computer simulation in reference
to the presence of CA in the arteries. As a result, 90 % of the contrast contribution is defined by 16 % of the symmetrically
acquired central k-space lines. A measuring protocol for clinical use was obtained by a gradual variation of spacial resolution,
measuring time and CA-injection parameters and was proved in normal volunteers and patients. An exact determination of the
bolus-arrival-time by means of a test-bolus injection was acquired. The best qualitative results were achieved by a double-dose
injection at 2 ml/s injection rate. The temporal reserves of ultra-fast sequences should be invested in the improvement of
the spatial resolution. To date, further investigations related to the problem of optimal CA-application may improve the potentials
of CE-MRA procedures.
相似文献
945.
Glutamine and Other Amino Acid Losses During Continuous Venovenous Hemodiafiltration 总被引:2,自引:0,他引:2
I. Novák V. rámek H. Pittrová Z. Ruavý P. Têinský S. Lacigová M. Eiselt L. Kohoutková E. Veselá K. Opatrný Jr. 《Artificial organs》1997,21(5):359-363
Abstract: Serum amino grams and daily losses of glutamine (Gin) and other amino acids (AAs) into diafiltrate were measured during the first 5 days of continuous venovenous hemodiafiltration (CVVHDF) in 6 ICU patients with acute renal failure (ARF). Four patients had ARF as a part of multiple organ failure (MOF) of septic origin, and 2 patients had isolated ARF because of primary renal disease. During the study, all the patients received defined total parenteral nutrition (TPN). The mean daily AA losses into dialysate were relatively low (0.61 ± 0.1 g N ) and reached 4.5% of the daily AA substitution. Gln represented 32.7 ± 5.9% of the total AA losses (0.19 ± 0.04 g N ). Serum levels of Gin (p = 0.002) and of most other AAs were significantly lower in the patients than in the control subjects (AA analysis in 16 healthy volunteers). Phenylalanine (Phe) was the only AA that was increased significantly (p < 0.01) in the patients. The mean patient serum concentrations of Phe and tyrosine were significantly higher (p < 0.03) than the correspondent concentrations in dialysate, but the lysine concentration was higher in dialysate (p < 0.03). The serum and dialysate concentrations of other AAs did not differ. Gin in serum decreased significantly (p < 0.03) on the second day of CVVHDF but returned to the baseline levels subsequently. Serum concentrations of Phe increased on the second day of CVVHDF (p < 0.05). Serum concentrations of other AAs remained stable during the whole study. We conclude that Gin losses into dialysate during CVVHDF are relatively low, but CVVHDF itself may induce changes in Gin metabolism and distribution that are reflected by a decrease of serum Gin levels at the institution of this treatment. Therefore, the need for Gin supplementation in ICU patients is even greater in the first days of CVVHDF. 相似文献
946.
947.
A. Newman-Tancredi V. Audinot V. Jacques J. L. Peglion M. J. Millan 《Neuropharmacology》1995,34(12):1693-1696
The selective dopamine D3 receptor antagonist [3H](+)S 14297 ((+)-[7-(N,N-dipropylamino)-5,6,7,8-tetrahydro-naphtho(2,3b)dihydro,2,3-furane]), labelled to high specific activity (145 Ci/mmol), bound to cloned human dopamine D3 receptors but displayed negligible binding to cloned human D2 receptors. [3H](+)S 14297 exhibited rapid association and dissociation, high affinity saturable binding (Kd = 7.0 nM) and a competition binding profile highly correlated with that of [125I]iodosulpride (r = 0.98). 相似文献
948.
949.
利用气相色谱—质谱—计算机联用仪分析了云南省腾冲县产珠子参挥发油的成份,从中鉴定了27种化合物,测定了它们的相对含量,其中有10种倍半萜烯和一种倍半萜醇。 相似文献
950.
Kaisa Heiskanen Pirjo Lindstr m-Sepp Leena Haataja Sirkka-Liisa Vaittinen Terttu Vartiainen Hannu Komulainen 《Toxicology》1995,100(1-3):121-128
Activities of the xenobiotic metabolizing enzymes were measured in the liver, kidney, duodenum and lung microsomes and cytosol fractions of Wistar rats after subchronic administration of 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX), a potent bacterial mutagen in chlorinated drinking water. MX was administered by gavage at the dose level of 30 mg/kg for 18 weeks (low dose), or at the dose level which was raised gradually from 45 mg/kg for 7 weeks via 60 mg/kg for 2 weeks to a clearly toxic dose of 75 mg/kg for 5 weeks (high dose). Microsomal and cytosolic preparations were made and the activities of 7-ethoxyresorufin-O-deethylase (EROD), pentoxyresorufin-O-dealkylase (PROD), NADPH-cytochrome-c-reductase, UDP-glucuronosyltransferase (UDPGT) and glutathione-S-transferase (GST) were measured. Kidneys were affected most. A dose-dependent decrease was observed in EROD (90% in males, 80% in females at the high dose) and in PROD (58% in females, at the high dose) in kidneys. An increase was, however, detected in kidney NADPH-cytochrome-c-reductase (66% in females at high dose), UDPGT (89% in males and 97% in females at high dose) and GST activities (56% in males and 50% in females at high dose). MX caused only a few changes in the enzyme activities of the liver. The EROD activity was decreased 25% to 37%, both in the livers of males and females, but the total content of P450s was not altered. Hepatic GST activity was elevated in females in a dose-dependent manner (31% and 44%). GST activity was elevated in duodenum in females (59%) at the high dose. There were no marked changes in the enzyme activities in the lungs. MX was a weak inhibitor of EROD activity both in the liver and kidney microsomes in vitro, decreasing the EROD activity by 53% and 43%, respectively at the concentration of 0.9 mM. The results indicate that MX decreases the activity of phase I metabolism enzymes, but induces phase II conjugation enzyme activities, particularly in kidneys in vivo. It is possible that these changes contribute to metabolism of MX in kidneys and renders them susceptible to MX in the course of repeated exposure. 相似文献