全文获取类型
收费全文 | 6057篇 |
免费 | 286篇 |
国内免费 | 7篇 |
出版年
2022年 | 38篇 |
2021年 | 64篇 |
2020年 | 31篇 |
2019年 | 50篇 |
2018年 | 90篇 |
2017年 | 59篇 |
2016年 | 125篇 |
2015年 | 172篇 |
2014年 | 203篇 |
2013年 | 526篇 |
2012年 | 353篇 |
2011年 | 380篇 |
2010年 | 228篇 |
2009年 | 236篇 |
2008年 | 392篇 |
2007年 | 413篇 |
2006年 | 368篇 |
2005年 | 409篇 |
2004年 | 388篇 |
2003年 | 412篇 |
2002年 | 326篇 |
2001年 | 57篇 |
2000年 | 31篇 |
1999年 | 67篇 |
1998年 | 88篇 |
1997年 | 72篇 |
1996年 | 63篇 |
1995年 | 54篇 |
1994年 | 56篇 |
1993年 | 60篇 |
1992年 | 45篇 |
1991年 | 36篇 |
1990年 | 39篇 |
1989年 | 24篇 |
1988年 | 28篇 |
1987年 | 16篇 |
1986年 | 17篇 |
1985年 | 24篇 |
1984年 | 23篇 |
1983年 | 20篇 |
1982年 | 31篇 |
1981年 | 48篇 |
1980年 | 31篇 |
1979年 | 20篇 |
1978年 | 13篇 |
1977年 | 15篇 |
1976年 | 14篇 |
1975年 | 18篇 |
1973年 | 12篇 |
1972年 | 10篇 |
排序方式: 共有6350条查询结果,搜索用时 15 毫秒
991.
Shibata Kenji Yano Keiichi Tanaka Takeo Matsuda Yuzuru Yamasaki Motoo 《International journal of peptide research and therapeutics》1997,4(3):167-170
Summary RES-701-1 is an endothelin B receptor (ETB) selective peptidic antagonist, which has a novel cyclic structure of microbial origin. Modification at the C-terminal free
carboxyl group of RES-701-1 by a methyl ester results in an ETA/ETB dual selective analog, which showed relatively high affinity for ETA receptor subtype, while retaining the affinity for ETB. The carboxyl-group-deleted analog with tryptamine as the C-terminal residue also showed relatively weak affinity for ETA; however, benzyl ester or amide analogs did not show remarkable affinity for ETA. It is suggested that the binding mode of RES-701-1 and its analogs is different from those of known ligands for ET receptors. 相似文献
992.
Abstract. We investigated the effect of topography‐related environmental factors (i.e., ground‐surface stability and soil moisture) on seedling establishment of 8 deciduous tree species. A field experiment was carried out using canopy species, which were classified into 3 groups based on the spatial distribution of adult trees (ridge, slope and valley). Demographic parameters were compared among species during the early stage of seedling establishment among 3 topographic positions in combination with gap and canopy conditions. The percentage of emerging seedlings tended to be lower on the ridge irrespective of the adult topographical distribution patterns. There was no clear trend in seedling emergence among the species groups classified by their spatial distribution. Seedling survival during 2 growing seasons was significantly different among species, topographic positions and light conditions. On the ridge, seedlings of the species dominating ridge tops had greater survival than those of other species, probably due to differences in demand for soil moisture. On the slope, frequent physical damage caused by surface material movement was observed and some species showed greater adaptability to the disturbed slope habitat. Survival of all seedlings was highest in the valley plots. Light conditions were the critical factor for seedling survival in some species. The results of this study suggest that topography creates diverse habitats for the establishment of tree seedlings. In addition to soil moisture, surface material movement may be a significant factor affecting seedling establishment. 相似文献
993.
Five glycosidase activities from cell homogenate of carrot ( Daucus carota L. cv. Kintoki) cell cultures were assayed after extraction successively by phosphate buffer (pH 7.0) and the buffer plus 2 M NaCl. A β-galactosidase (EC 3.2.1.23) was isolated in a highly purified state from the buffer-soluble protein fraction by ammonium sulfate fractionation and chromatography on CM-Sephadex C-50, DEAE-Sephadex A-50 and Sephadex G-200. The molecular weight of this enzyme was ca 104 000 and the isoelectric point was pH 7.8. The optimal activity occurred at pH 4.4 with McIlvaine buffer. The Km and Vmax values were 1.67 m M and 201 units (mg protein)−1 , respectively, for p -nitrophenyl β- d -galactopyranoside. The enzyme activity was strongly inhibited by Zn2+ , Cu2+ , Hg2+ and d -galactono-1,4-lactone. The enzyme acted on the β-1,4-linked galactan prepared from citrus pectin in an exo-fashion. Furthermore, the enzyme was slightly involved in the hydrolysis of the pectic polymer and cell walls purified from carrot cell cultures. 相似文献
994.
This is the first report on the annual egg production patterns in mature termite colonies in the field. Data on the seasonal
patterns of egg production in field colonies are very important for understanding the annual colony growth schedule, resource
allocation, and population dynamics of the termites. However, collecting the eggs from a sufficient number of colonies is
extremely difficult in Reticulitermes termites because their multiple-site nesting makes it difficult to find the reproductive center of the colonies. Here, we
first show the seasonal pattern of egg production in the subterranean termite Reticulitermes speratus by collecting the reproductive center of ten colonies each month from April through October. We had to destructively examine
dozens of nests to find eggs from enough field colonies each month. Mature field colonies began to produce eggs in late May,
soon after the swarming season, and the egg production rate (EPR) reached its maximum in early July. The eggs hatched until
late October. The EPR was significantly correlated with the average monthly temperature. Additional investigation of the egg
distributions in the nests showed that most eggs were kept around the royal cell, which contained the reproductives. The largest
colony had 109 supplemental queens and 94,023 eggs, suggesting that each queen produced an average of 24.7 eggs per day, based
on the known mean hatching period of an inseminated egg of 34.95±0.12 (SE) days. 相似文献
995.
Geographic variation in diapause induction under constant and changing conditions in Helicoverpa armigera 总被引:1,自引:0,他引:1
Variation in the incidence of diapause in local populations of Helicoverpa armigera (Hübner) and Helicoverpa assulta (Guenée) (Lepidoptera: Noctuidae) was examined in relation to changes in photoperiod and/or temperature during the larval period. Temperate zone populations of H. assulta, a native species in temperate Japan, showed a high incidence of diapause induction when only the photoperiod was decreased during the larval period, even at favorable temperatures. This photoperiod‐dependent response may allow H. assulta to foresee the beginning of autumn well in advance in the temperate zone, where temperature conditions are severe. In contrast, temperate zone populations of H. armigera, an invasive and polyphagous species mainly distributed in the subtropics, showed a high incidence of diapause only when both photoperiod and temperature decreased, whereas subtropical populations showed a very low incidence of diapause under the same conditions. Furthermore, both temperate zone and subtropical populations of H. armigera enter diapause under constant low temperatures at short‐day photoperiod. Thus, there is geographic variation in sensitivity to diapause‐inducing stimuli (changes in photoperiod and temperature) in H. armigera. This variation may be a part of the climatic adaptation achieved by H. armigera in Japan. 相似文献
996.
Yoshihiro Itoh Satoshi Horiuchi Kenji Yamamoto 《Photochemical & photobiological sciences》2005,4(10):835-839
A series of benzyl-containing ammonium salts, p-alkylbenzyltrimethylammonium halides (C(n)BA: 1a-c) and alkylbenzyldimethylammonium halides (C(n)AB: 2a-d), have been prepared and their photodegradabilities in aqueous solutions have been compared. The photolytic decomposition proceeded by heterolytic and homolytic cleavages of the benzyl-nitrogen bond. The conversion yields were almost the same for all surfactants, whereas the product yields were slightly dependent on the alkyl-chain length. After irradiation, C(8)BA (1b) and C(12)BA (1c) were converted to non-surfactants, whereas C(12)AB (2c) and C(16)AB (2d) still remained surface-active. Their solution properties were concomitantly changed. 相似文献
997.
Celina M Haraguchi Tadashi Mabuchi Shuji Hirata Tomoko Shoda Kazuhiko Hoshi Kenji Akasaki Sadaki Yokota 《The journal of histochemistry and cytochemistry》2005,53(4):455-465
We investigated the localization of several markers for lysosomes and aggresomes in the chromatoid bodies (CBs) by immunoelectron microscopy. We found so-called aggresomal markers such as Hsp70 and ubiquitin in the core of the CBs and vimentin and proteasome subunit around the CBs. Ubiquitin-conjugating enzyme (E2) was also found in the CBs. In tubulovesicular structures surrounding the CBs, lysosomal markers were detected but an endoplasmic reticulum retention signal (KDEL) was not. Moreover, proteins located in each subcellular compartment, including the cytosol, mitochondria, and nucleus, were detected in the CBs. Signals for cytochrome oxidase I (COXI) coded on mitochondrial DNA were also found in the CBs. Quantitative analysis of labeling density showed that all proteins examined were concentrated in the CBs to some extent. These results show that the CBs have some aggresomal features, suggesting that they are not a synthetic site as proposed previously but a degradation site where unnecessary DNA, RNA, and proteins are digested. 相似文献
998.
Mori Toyoki Takeuchi Tadayoshi Ohura Makoto Miyakoda Goro Fujiki Hiroyuki Orito Kensuke Yoshida Kenji Hirano Takahiro Yamamura Yoshitaka Sumida Takumi Nakaya Yutaka Satake Hiromu Hata Fumiaki 《Molecular and cellular biochemistry》1998,178(1-2):335-343
Pranidipine, a new calcium channel modulator, prolonged endothelium-dependent relaxation induced by acetylcholine in a aortic ring preparation, contracted with prostaglandin F2. This action was not shared by amlodipine. The effect was not modified by indomethacin, suggesting that the action of pranidipine does not involve prostanoid metabolism. NG-nitro-L-arginine completely prevented the action of Pranidipine. The drug affected neither nitric oxide (NO) synthase activity nor the level of cyclic GMP in the vessel. Pranidipine did not affect the sensitivity of the contractile proteins to calcium. Pranidipine also did not alter cyclic GMP-induced relaxation in a-toxinskinned vascular preparations. Pranidipine also prolonged glyceryl trinitrate-induced relaxation in the endothelium denuded rat aorta. Furthermore, pranidipine enhanced relaxation of the aorta induced by glyceryl trinitrate even in the presence of methylene blue, a guanylyl cyclase inhibitor. This action was not modified by iberiotoxin or by charybdotoxin, two inhibitors of the calciumactivated potassium channel. The results strongly suggest that pranidipine enhances cyclic GMPindependent NO-induced relaxation of smooth muscle by a mechanism other than through NOinduced hyperpolarization. These effects were in direct contrast to amlodipine, another new 1,4dihydropyridine calcium antagonist. 相似文献
999.
One hundred sixty-six isolates of Fusarium spp. from domestic cereal grains, feed, and other sources were examined for their ability to produce zearalenone on autoclaved moist rice grains. They belonged to the following species (number of producers/number tested): F. roseum (9/28), F. roseum (Culmorum) (3/4), F. roseum (Gibbosum) (2/5), F. roseum (Avenaceum) (1/2), F. roseum (Scirpi) (0/1), F. tricinctum (1/4), F. tricinctum (Sporotrichiella) (0/7), F. lateritium (1/1), F. episphaeria (0/2), F. moniliforme (0/3), F. oxysporum (0/12), F. rigidiusculum (0/4), F. solani (0/4), F. splendens (0/1), F. nivale (0/2), and Fusarium spp. (15/86). Zearalenone was isolated from molded rice by ethanol extraction and purified by column chromatography. Selected isolates of F. roseum M-3-2 and F. roseum (Gibbosum) A-O-2 produced 50 to 100 mg of zearalenone per kg of rice. Increased yields (250 to 407 mg/kg of rice) were obtained by F. roseum M-3-2 when the substrate was supplemented with 1% peptone. 相似文献
1000.
Production of the Hepatotoxic Chlorine-Containing Peptide by Penicillium islandicum Sopp 总被引:2,自引:2,他引:0
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)
Twenty-six strains of Penicillium islandicum Sopp were tested for production of a chlorine-containing peptide (Cl-peptide), which is a hepatotoxin. Highest levels of the mycotoxin were produced in a modification of Wickerham medium. The mycotoxin was isolated by adsorption on charcoal and, after washing the charcoal with acetone-water (1:1), was eluted into n-butanol. Further purification was accomplished by gel filtration. Maximum yields were 10 to 20 mg of toxin per liter of culture filtrate. 相似文献