全文获取类型
收费全文 | 3254篇 |
免费 | 330篇 |
出版年
2023年 | 19篇 |
2022年 | 28篇 |
2021年 | 80篇 |
2020年 | 42篇 |
2019年 | 50篇 |
2018年 | 58篇 |
2017年 | 44篇 |
2016年 | 64篇 |
2015年 | 135篇 |
2014年 | 130篇 |
2013年 | 171篇 |
2012年 | 202篇 |
2011年 | 212篇 |
2010年 | 114篇 |
2009年 | 121篇 |
2008年 | 152篇 |
2007年 | 157篇 |
2006年 | 146篇 |
2005年 | 136篇 |
2004年 | 117篇 |
2003年 | 104篇 |
2002年 | 95篇 |
2001年 | 70篇 |
2000年 | 58篇 |
1999年 | 65篇 |
1998年 | 40篇 |
1997年 | 38篇 |
1996年 | 22篇 |
1995年 | 21篇 |
1993年 | 24篇 |
1992年 | 48篇 |
1991年 | 45篇 |
1990年 | 56篇 |
1989年 | 47篇 |
1988年 | 38篇 |
1987年 | 36篇 |
1986年 | 33篇 |
1985年 | 36篇 |
1984年 | 25篇 |
1983年 | 33篇 |
1982年 | 41篇 |
1981年 | 22篇 |
1980年 | 19篇 |
1979年 | 30篇 |
1978年 | 35篇 |
1977年 | 25篇 |
1976年 | 25篇 |
1975年 | 17篇 |
1974年 | 16篇 |
1973年 | 23篇 |
排序方式: 共有3584条查询结果,搜索用时 31 毫秒
61.
62.
Israel Zilbermann Maya Winnik Dalia Sagiv Amira Rotman Haim Cohen Dan Meyerstein 《Inorganica chimica acta》1995,240(1-2):503-514
The effects of N-alkylation on the redox potential of the couples NiLi2+/NiLi+, L = tetraaza-14-membered-macrocyclic ligands, and on the properties of the monovalent nickel complexes in aqueous solutions are reported for 14 complexes. The spectra and lifetimes of the NiLi+ complexes are reported. The self-exchange rates for the couples NiLi2+/NiLi+ were determined. Two of the ligands were synthesized for the first time for this study. Cyclic voltammetry and pulse radiolysis were used. The results point out that: (i) N-alkylation always shifts the redox potential to a less cathodic one; this effect stems to a large degree from the decrease in the solvation energy of the complex caused by the N-alkylation of the ligand. (ii). The lifetime of the monovalent complexes is not linearly related to the redox potential of the NiLi2+/NiLi+ couples. (iii) The NiLi+ complexes exist in several isomeric forms; the rate of the isomerization depends on the structure of the ligand. (iv) Different isomers of NiLi+ may be formed when the complex NiLi2+ is reduced by different reagents; therefore, the pulse-radiolytically formed NiLi+ complexes might have different properties than those formed electrochemically. 相似文献
63.
Michael J. Seckl Richard H. Newman Paul S. Freemont Enrique Rozengurt 《Journal of cellular physiology》1995,163(1):87-95
The substance P (SP) analogues [DArg1, DPhe5, DTrp7,9, Leu11] SP (AntD) and [Arg6, DTrp7,9, MePhe8] SP (6–11) (AntG) inhibit the action of many different neuropeptides including SP. These analogues might be useful in the treatment of small cell lung cancer but their mechanism of action is unclear. Here, we analyzed the effect of AntD and AntG on neuropeptide vs. guanosine 5′-3-O-(thio) triphosphate (GTPγS) stimulated inositol phosphate generation in permeabilized Swiss 3T3 cells. AntD inhibited vasopressin and bombesin stimulated inositol phosphate formation (IC50 of 0.75 μM and 2 μM, respectively). Similarly, AntG inhibited vasopressin-stimulated inositol phosphate generation with an IC50 of 1 μM. Strikingly, neither AntD up to 10 μM nor AntG up to 20 μM was able to inhibit GTPγS-stimulated inositol phosphate generation. Dose-response curves of neuropeptide-induced inositol phosphate generation were dramatically displaced to the right by either 10 μM AntD or 20 μM AntG. However, neither antagonist affected the dose response of GTPγS-stimulated inositol phosphate generation. Furthermore, 20 μM AntD had no effect on AIF?4-induced inositol phosphates in COS-1 cells transfected with Gαq. AntD inhibited [3H]vasopressin binding competitively in intact Swiss 3T3 cells and both AntD and AntG inhibited [3H]vasopressin binding in Swiss 3T3 and rat liver membranes. Scatchard analysis revealed that AntD inhibited vasopressin binding by reducing receptor affinity without affecting receptor number in both intact and membrane preparations of Swiss 3T3 cells. The results strongly suggest that SP analogues AntD and AntG block the action of the Ca2+ mobilizing neuropeptides at the receptor level, rather than inhibiting G protein-stimulated inositol phosphate production. © 1995 Wiley-Liss, Inc. 相似文献
64.
P. E. McAllister M. W. Newman J. H. Sauber W. J. Owens 《Helgoland Marine Research》1984,37(1-4):317-328
Two significant fish kills occurred in the Pamlico River estuary (North Carolina, USA), one in December 1981 and January 1982, and the other in June 1982. The first involved only the southern flounder(Paralichthys lethostigma). Histopathologic examination of morbid and moribund flounder revealed extensive sloughing and necrosis of the mucosa of the pyloric caeca and intestine, and inflammation of the submucosa of the pyloric caeca. Brain and internal organ homogenates from morbid and moribund flounder were assayed on CHSE-214 cells, and a virus was isolated. Virus titers ranged from8.4 · 102 to 6.3 · 107 TCID50 per gram of tissue. Cross-plaque neutralization assays indicated that the southern flounder virus was infectious pancreatic necrosis virus serotype Ab. Immersion challenge showed the isolate is only slightly virulent for fry of brook trout(Salvelinus fontinalis). The second fish kill involved the southern flounder and six other species: hogchoker(Trinectes maculatus), Atlantic silverside(Menidia menidia), spot(Leiostomus xanthurus), Atlantic croaker(Micropogon undulatus), silver perch(Bairdiella chrysura), and striped mullet(Mugil cephalus). Virus was isolated from southern founder, hogchoker, Atlantic silverside, and spot. Neutralization assays indicated that the four isolates were nearly identical; however, the diversity of species affected suggests that the virus might not have been the specific cause of mortality. 相似文献
65.
Ontario is home to a sizeable, recently established immigrant population whose cancer mortality has until now remained unexamined. The province''s six largest immigrant groups (British, Italian, German, Dutch, Polish and Soviet) were investigated to compare their cancer mortality experience with that prevailing in Ontario and in their countries of birth for the period 1969 through 1973. Standardized mortality ratios (SMRs) were computed from data from Statistics Canada and the World Health Organization (for 1971) for five sites of cancer. The rates of death from stomach cancer were significantly higher for the immigrant groups (except the Germans) than for the Canadian-born (SMRs 158.6 to 256.1) and were significantly lower for the immigrants (except the Dutch) than for the populations of their countries of birth (SMRs 26.5 to 72.9). The rates of death from colorectal cancer and cancer of the breast tended to be lower among the immigrants. Most male immigrants had high rates of death from lung cancer relative to the Canadian-born, whereas their female counterparts had relatively low rates. For most of the immigrant groups the rates of death from prostate cancer closely resembled those prevailing in the country of birth. Displacement of cancer mortality experience towards that in Ontario was most evident for Polish immigrants. It may have been too soon to see trends among the more recent immigrants (Italian, German and Dutch), who, for the most part, had not yet reached the age of highest cancer risk. Ontario should provide a valuable resource for further studies of lifestyle and environmental determinants of cancer. 相似文献
66.
67.
Inactivation rates of polioviruses 1 and 3 and coxsackieviruses A-13 and B-1 were determined in situ in the Rio Grande in southern New Mexico, using membrane dialysis chambers. Inactivation of the viruses was exponential, and the rates of inactivation were apparently affected principally by the water temperature. Stability of the viruses in river water differed, with poliovirus 1 and coxsackie B-1 being most stable. Typically 1-log reductions of infectivity at water temperatures ranging between 23 and 27 degrees C required 25 h for poliovirus 1, 19 h for poliovirus 3, and 7 h for coxsackie virus A-13. At water temperatures of 4 to 8 degrees C, the log reduction times for poliovirus 1 and coxsackievirus B-1 were 46 and 58 h, respectively. Results obtained with labeled poliovirus 1 and coxsackievirus B-1 and with infectious ribonucleic acid indicate that inactivation was due to damage to viral ribonucleic acid. Virus-inactivation rates were also affected by heat sterilization of river water, indicating the presence of a heat-labile or volatile inactivating factor. The inactivating factor in Rio Grande water was apparently present at a constant concentration over a 1-year period. 相似文献
68.
69.
Structural and compositional changes associated with chlorine inactivation of polioviruses. 总被引:8,自引:7,他引:1
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Chlorine inactivation of polioviruses resulted in the loss of viral ribonucleic acid, converting the viruses from 156S particles to 80S particles. However, it was found that virus inactivation occurred before the ribonucleic acid was released from the virions. Extraction of ribonucleic acid from partially inactivated virus suspensions indicated that chlorine inactivation was due to degradation of the ribonucleic acid before release and that ribonucleic acid loss was a secondary event. The empty 80S capsids had the same isoelectric point and ability to attach to host cells as infective virions. Thus, no major capsid conformational changes occurred during chlorine inactivation. 相似文献
70.
To determine if neural crest cells are pluripotent and establish whether differentiation occurs in the absence of noncrest cells, a cell culture method was devised in which differentiation could be examined in clones derived from single, isolated neural crest cells. Single neural crest cells, which were isolated before the onset of in vivo migration, gave rise to three types of clones: pigmented, unpigmented, and mixed. Pigmented clones consisted of melanocytes only, whereas some unpigmented cells in mixed and unpigmented clones contained catecholamines, identifying them as adrenergic cells. Extracellular matrix derived from quail somite or chick skin fibroblast cultures stimulated adrenergic differentiation and axon formation. These results demonstrate for the first time the existence of pluripotent quail neural crest cells that give rise to at least two progeny, melanocytes and neuronal cells. They also suggest that continuous direct interactions with noncrest cells are not required for the differentiation of these two cell types. However, components of the extracellular matrix derived from noncrest cells may play an important role in expression of the adrenergic phenotype. 相似文献