全文获取类型
收费全文 | 55027篇 |
免费 | 4640篇 |
国内免费 | 36篇 |
专业分类
59703篇 |
出版年
2023年 | 268篇 |
2022年 | 579篇 |
2021年 | 1053篇 |
2020年 | 770篇 |
2019年 | 836篇 |
2018年 | 1206篇 |
2017年 | 1006篇 |
2016年 | 1642篇 |
2015年 | 2355篇 |
2014年 | 2311篇 |
2013年 | 2879篇 |
2012年 | 3428篇 |
2011年 | 3162篇 |
2010年 | 1931篇 |
2009年 | 1873篇 |
2008年 | 2289篇 |
2007年 | 2269篇 |
2006年 | 2062篇 |
2005年 | 2374篇 |
2004年 | 2352篇 |
2003年 | 1960篇 |
2002年 | 1582篇 |
2001年 | 1466篇 |
2000年 | 1392篇 |
1999年 | 1250篇 |
1998年 | 580篇 |
1997年 | 550篇 |
1996年 | 600篇 |
1995年 | 466篇 |
1994年 | 468篇 |
1993年 | 441篇 |
1992年 | 936篇 |
1991年 | 834篇 |
1990年 | 775篇 |
1989年 | 766篇 |
1988年 | 761篇 |
1987年 | 691篇 |
1986年 | 648篇 |
1985年 | 633篇 |
1984年 | 585篇 |
1983年 | 446篇 |
1982年 | 343篇 |
1981年 | 335篇 |
1980年 | 316篇 |
1979年 | 439篇 |
1978年 | 365篇 |
1977年 | 305篇 |
1975年 | 302篇 |
1974年 | 304篇 |
1973年 | 301篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
171.
Isolation and characterization of Pediococcus halophilus from salted anchovies (Engraulis anchoita) 总被引:3,自引:0,他引:3
M Villar A P de Ruiz Holgado J J Sanchez R E Trucco G Oliver 《Applied and environmental microbiology》1985,49(3):664-666
The presence of bacteria in salted anchovies during and at the end of the curing process was investigated. Attempts to isolate bacteria under aerobic or anaerobic conditions led to the isolation of only bacteria of the genus Pediococcus which were identified as Pediococcus halophilus. The isolates correspond to a rather heterogeneous group in which some of the members differ in some biochemical tests from the types described in the literature. 相似文献
172.
A prospective study with mild general analgesia and sedation together with local anesthesia during bone marrow harvest was performed. Thirty-one patients underwent 33 bone marrow collections. Pretreatment consisted of 100 mg meperidine i.m. and 20 mg diazepam i.m. 1 h before start of procedure. Eight patients got additional meperidine and diazepam during the procedure, all patients got lidocaine 1% locally. A mean volume of 1.321 was obtained with 42.5 punctures. Twenty-two patients had no complications, 4 vomited, 4 had easily correctable hypotension of short duration, one got oxygen for cyanosis of short duration. Acceptance was good in 23 patients, in 6 reasonably well, in two bad. Only one patient experienced pain problems, due to suction. Anxiety was no major problem due to good information before the procedure and mild sedation. This form of anesthesia for bone marrow collection is a safe procedure, it is generally well accepted by the patient and it can be performed on an out-patient basis. 相似文献
173.
N H Fraeyman F H De Smet E J Van de Velde E J Moerman A F De Schaepdryver 《Life sciences》1984,35(6):619-629
The murine C1300 neuroblastoma tumor was found to secrete dopamine, noradrenaline and dopamine B-hydroxylase into the circulation of tumor-bearing A/J mice. The plasma levels of dopamine, noradrenaline and dopamine B-hydroxylase increased with the size of the tumor, and the increase in noradrenaline paralleled the increase in dopamine B-hydroxylase (r = 0.86). The vesicular storage of dopamine and noradrenaline in the tumor was evidenced by a decrease of the tissue content of dopamine and noradrenaline 24 hours after the administration of reserpine (5 micrograms/g) respectively to 17.6% and 7.8% of control values. A similar observation could be made for the levels of dopamine and noradrenaline in the plasma of reserpinized C1300 mice. The total activity of dopamine B-hydroxylase in the tumor and in plasma was unaffected by the reserpine treatment. Chronic administration of 6-hydroxydopamine (100 micrograms/g for 8 days) had no effect on the tissue contents of dopamine, noradrenaline or dopamine B-hydroxylase. The release of catecholamines and dopamine B-hydroxylase from the C1300 neuroblastoma was studied in vitro on superfused tumor slices. Stimulation of these slices with 56 mM KC1 or with 5.10(-5) M tyramine failed to induce the release of endogenous dopamine, noradrenaline or dopamine B-hydroxylase above the basal outflow levels. These results are suggestive for a non-exocytotic release of catecholamines and dopamine B-hydroxylase from the neuroblastoma tumor. 相似文献
174.
Depending on the species, Cryptocoryne plants grow in different biotopes, viz. spring, river, dark forest, and tree-savanna. The species of Lagenandra are exclusively found in river biotopes. The chromosome numbers found in this study corroborate the numbers previously recorded. Some variation in respect to the morphology of the inflorescence of C. wendtii de Wit and L. ovata (L.) Thwaites is described. A map presenting the distribution of the of Cryptocoryne with their chromosome numbers is included.
The existing populations of Cryptocoryne on Sri Lanka should be protected from further exploitation by plant collectors. 相似文献
The existing populations of Cryptocoryne on Sri Lanka should be protected from further exploitation by plant collectors. 相似文献
175.
176.
177.
C. G. van Ginkel H. G. J. Welten J. A. M. de Bont 《Applied microbiology and biotechnology》1986,24(4):334-337
Summary Newly isolated Xanthobacter spp. were able to grow on the gaseous alkenes like ethene, propene, 1-butene and 1,3-butadiene. Resting-cell suspensions of propene-, 1-butene- or 1,3-butadiene-grown Xanthobacter Py10 accumulated 1,2-epoxyethane from ethene. Ethene-grown Xanthobacter Py10 did not produce any 1,2-epoxyalkane from the alkenes tested. Furthermore, propenegrown Xanthobacter Py2 accumulated 2,3-epoxybutane from trans-butene and cis-butene but did not form epoxides from other substrates tested. 相似文献
178.
IMP production and energy metabolism during exercise in rats in relation to age. 总被引:1,自引:0,他引:1 下载免费PDF全文
IMP production in and force exerted by rat quadriceps muscle in situ during various types of exercise were examined in relation to age. During continuous isometric exercise with constant stimulation time, the amount of IMP was linearly and inversely related to the age of the animals; a higher IMP concentration was found in intermittent isometric and dynamic exercise. No relationship was found between the total AMP deaminase activity and age. Exercise influenced neither the total activity nor the activity in the soluble fraction. From the results it is concluded that: the IMP concentration is linearly related to the free intracellular ATP4-/ADP3- ratio and the free AMP2- concentration; older animals are better able to maintain a high intramuscular ATP4-/ADP3- ratio and a low AMP2- concentration; IMP is produced in particular under conditions when the muscle has to work under extreme stress. IMP possibly exerts a feed-back control on the contraction system. 相似文献
179.
Changes in erythropoiesis due to radiation or chemotherapy as studied by flow cytometric determination of peripheral blood reticulocytes 总被引:1,自引:0,他引:1
H J Tanke P H van Vianen F M Emiliani I Neuteboom N de Vogel A D Tates E A de Bruijn A T van Oosterom 《Histochemistry》1986,84(4-6):544-548
Flow cytometric determination of time dependent changes of numbers of reticulocytes in peripheral blood were investigated as a parameter for changes in erythropoiesis induced by radiation- or chemotherapy. Rats irradiated or treated with drugs (such as e.g. cyclophosphamide 100 mg/kg, vincristin 0.2 mg/kg, or mitomycin C 1.0 mg/kg) showed clear changes in erythropoietic activity. Reticulocyte numbers decreased rapidly until day 3-4 after treatment; this period was followed by a gradual increase and normal control values were seen at day 8-11. Radiation effects of doses as low 0.5 Gy could be detected in such a way. Similar studies were performed with patients with ovarian tumors treated with cis-platinum, a drug that may cause non-immune haemolysis. During prolonged treatment some patients showed increasing numbers of reticulocytes, measured at the first day of each hospitalization period, whereas leucocyte and platelet counts stayed more or less constant. Increasing numbers of reticulocytes generally indicates stimulation of erythropoietic activity of the bone marrow (due to increased blood loss); in this study increasing numbers often preceeded a decrease in hemoglobin values later on. Flow cytometric analysis of reticulocytes is therefore a potentially useful tool to detect changes in erythropoiesis, and considered more sensitive for the early recognition of patients that develop anemia, than hemoglobin measurements only. 相似文献
180.
Summary An isochromosome of 15(q12) was found in a mentally retarded patient with behaviour disorders which included hyperactivity, short attention span, aggression, and autistic behaviour. There were only minor physical anomalies; he did not have the Prader-Willi syndrome. 相似文献