全文获取类型
收费全文 | 11935篇 |
免费 | 683篇 |
国内免费 | 35篇 |
出版年
2024年 | 18篇 |
2023年 | 113篇 |
2022年 | 355篇 |
2021年 | 605篇 |
2020年 | 359篇 |
2019年 | 460篇 |
2018年 | 507篇 |
2017年 | 377篇 |
2016年 | 533篇 |
2015年 | 628篇 |
2014年 | 745篇 |
2013年 | 926篇 |
2012年 | 989篇 |
2011年 | 886篇 |
2010年 | 523篇 |
2009年 | 424篇 |
2008年 | 544篇 |
2007年 | 510篇 |
2006年 | 467篇 |
2005年 | 454篇 |
2004年 | 350篇 |
2003年 | 295篇 |
2002年 | 260篇 |
2001年 | 124篇 |
2000年 | 114篇 |
1999年 | 95篇 |
1998年 | 67篇 |
1997年 | 42篇 |
1996年 | 42篇 |
1995年 | 48篇 |
1994年 | 32篇 |
1993年 | 37篇 |
1992年 | 58篇 |
1991年 | 51篇 |
1990年 | 60篇 |
1989年 | 46篇 |
1988年 | 47篇 |
1987年 | 36篇 |
1986年 | 35篇 |
1985年 | 40篇 |
1984年 | 35篇 |
1983年 | 31篇 |
1982年 | 26篇 |
1981年 | 30篇 |
1980年 | 19篇 |
1979年 | 17篇 |
1978年 | 22篇 |
1977年 | 20篇 |
1976年 | 24篇 |
1975年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 529 毫秒
121.
122.
Copper metabolism in a teleost, the plaice, Pleuronectes platessa (L.) from a natural environment has been studied. Distribution in the various tissues of the metal and of five key copper-dependent enzymes: ceruloplasmin EC 1.16.3.1; Superoxide dismutase EC 1.15.11; tryptophan oxygenase EC 1.13.1.12; cytochrome oxidase EC 1.9.3.1 and monoamine oxidase EC 1.4.3.4 have been determined. The copper distribution was found to be similar to that in mammals with the greatest concentrations in the brain and heart. Distribution of the copper enzymes is also similar to that found in mammals. A preliminary characterization of the copper enzymes showed that plaice cytochrome oxidase has a pH maximum 2 pH units more alkaline than the mammalian enzyme and that plaice tryptophan oxygenase is more sensitive to heat denaturation than the mammalian enzyme. The present data form a base-line against which studies on factors affecting the copper metabolism in a teleost can be assessed. 相似文献
123.
A new class of therapeutic agents, sharing inhibition of the slow calcium channel, will soon be available to the American patient. Selective action of these agents upon the atrioventricular node, the smooth muscle of coronary and peripheral arteries, and the contractility of cardiac muscle opens new vistas in cardiovascular pharmacology. Early release of these agents by the Federal Drug Administration for general use is urged, based upon the already wide and successful experience in the European and South American continents. 相似文献
124.
Bovine gastric mucosal and muscle microsomes synthesize prostaglandins and thromboxane B2 (TXB2) from arachidonic acid (AA). TXB2 and 6-keto-prostaglandin F1α (6-keto-PGF1α) were the major products synthesized by pylorus, body, and cardiac region of the gastric mucosa. Gastric muscle mainly synthesized 6-keto-PGF1α. TXB2 and 6-keto-PGF1α synthesis occurs at an appreciable rate from endogenous precursors but more rapidly with added arachidonate. Prostaglandins E2, F2α and D2 were synthesized in smaller amounts under the conditions studied. 相似文献
125.
126.
Ali E. Engin Richard D. Peindl Vasundara V. Varadan Vijay K. Varadan 《Journal of biomechanics》1980,13(12):1053-1059
This investigation is concerned with a scattering matrix approach which is proposed for the non-destructive, differential diagnosis of muscle diseases. A number of muscle diseases are classified according to their various pathological indications and appropriate material parameters are derived for utilization as input data for a theoretical model. In the mathematical analysis phase of the model, Waterman's T-matrix approach in conjunction with statistical averaging for both position and orientation of muscle fibers are employed to obtain the attenuation due to geometric dispersion for a wide range of frequencies. The numerical results not only exhibit qualitative agreement with existing experimental data for normal muscle but also display differentiable patterns for the various muscle disease cases. The formulation is an improvement over the previously applied scattering theory in that it obtains the attenuation over a continuous frequency spectrum. 相似文献
127.
128.
The role of chlorinated primary effluents in viral pollution of the Ottawa River (Ontario) was assessed by examining 282 field samples of wastewaters from two different sewage treatment plants over a 2-year period. The talc-Celite technique was used for sample concentration, and BS-C-1 cells were employed for virus detection. Viruses were detected in 80% (75/94) of raw sewage, 72% (68/94) of primary effluent, and 56% (53/94) of chlorinated effluent samples. Both raw sewage and primary effluent samples contained about 100 viral infective units (VIU) per 100 ml. Chlorination produced a 10- to 50-fold reduction in VIU and gave nearly 2.7 VIU/100 ml of chlorinated primary effluent. With a combined daily chlorinated primary effluent output of approximately 3.7 × 108 liters, these two plants were discharging 1.0 × 1010 VIU per day. Because the river has a mean annual flow of 8.0 × 1010 liters per day, these two sources alone produced a virus loading of 1.0 VIU/8 liters of the river water. This river also receives at least 9.0 × 107 liters of raw sewage per day and undetermined but substantial amounts of storm waters and agricultural wastes. It is used for recreation and acts as a source of potable water for some 6.0 × 105 people. In view of the potential of water for disease transmission, discharge of such wastes into the water environment needs to be minimized. 相似文献
129.
130.
Synopsis The histochemical localization of carbohydrates, ribonucleoproteins (RNA), lipids, some hydrolytic enzymes, succinate and lactate dehydrogenase and acetylcholinesterase were investigated in the prostate, urethral and bulbourethral glands of the camel. These glands probably secrete carbohydrate-protein complexes. In the bulbourethral glands, they are sulphated mucopolysaccharides. RNA was seen in the cytoplasm of the prostate and urethral glands. Neutral lipids were cytoplasmic and present in moderate amounts in the prostate and urethral glands and in traces, in the bulbourethral gland. Acid phosphatase-containing granules were abundant in the prostate, moderate in the urethral glands and in traces in the bulbourethral glands. Alkaline phosphatase was observed in the apical cytoplasm of the prostate and bulbourethral glands and in the ducts of the urethral glands. ATPase and adenosine 5-monophosphatase were seen in the basal laminae and interstitial tissue. In the urethral glands, adenosine 5-monophosphatase was distributed diffusely in the cytoplasm. Succinate dehydrogenase was seen in the urethral and bulbourethral glands. Varying degrees of lactate dehydrogenase activity was observed in all the glands. Acetylcholinesterase was confined to neural elements. The pars disseminata and the urethral glands were considered as two distinct glandular zones along the pelvic urethra. The significance of these histochemical results is discussed. 相似文献